Online Etymology Dictionary

impracticality (n.): 1843; see impractical + -ity.
imprecate (v.): "call down by prayer" (typically of curses or malevolent desires), 1610s, probably a back-formation from imprecation. Related: Imprecated; imprecating; imprecatory (1580s).
imprecation (n.): mid-15c., "a curse, cursing," from Latin imprecationem (nominative imprecatio) "an invoking of evil," noun of action from past participle stem of imprecari "invoke, pray, call down upon," from assimilated form of in- "into, in, within" (see in- (2)) + precari "to pray, ask, beg, request" (see pray). "Current limited sense is characteristic of human nature" [Weekley].
imprecise (adj.): 1804, from assimilated form of in- (1) "not, opposite of" + precise. Earlier was unprecise (1756). Related: Imprecisely.
imprecision (n.): "inexactness," 1771, from assimilated form of in- (1) "not, opposite of" + precision.
impregnability (n.): 1755, from impregnable + -ity.
impregnable (adj.): early 15c., imprenable "impossible to capture," from Old French imprenable "invulnerable," from assimilated form of in- "not, opposite of" (see in- (1)) + Old French prenable "assailable, vulnerable" (see pregnable). With restored -g- from 16c. Related: Impregnably.
impregnate (v.): c. 1600, "to fill with an ingredient, spirit, etc.;" 1640s as "make (a female) pregnant), from Late Latin impraegnatus "pregnant," past participle of impraegnare "to render pregnant," from assimilated form of in- "into, in" (see in- (2)) + praegnare "make pregnant" (see pregnant). Earlier in same sense was impregn (1530s), which OED marks as "now only in poetic use."
impregnation (n.): late 14c., "making or becoming pregnant," from Old French impregnacion or directly from Late Latin impregnationem (nominative impregnatio), noun of action from past participle stem of impraegnare "to impregnate" (see impregnate).
impresario (n.): "one who organizes public entertainments," 1746, from Italian impresario "operatic manager," literally "undertaker (of a business)," from impresa "undertaking, enterprise, attempt," fem. of impreso, past participle of imprendere "undertake," from Vulgar Latin imprendere, from assimilated form of in- "into, in, on, onto" (see in- (2)) + prehendere "to grasp" (see prehensile).
imprescriptible (adj.): "inalienable, not subject to law or convention," 1560s, from French imprescriptible (16c.) or a native formation from assimilated form of in- (1) "not, opposite of" + Latin praescriptus, past participle of praescribere "to write beforehand, determine in advance, ordain, dictate" (see prescribe). Usually with right (n.). Related: Imperscriptibility. Alternative imprescribable is attested from 1887.
impress (v.1): late 14c., "have a strong effect on the mind or heart, to stamp deeply in the mind," from Latin impressus, past participle of imprimere "press into or upon, stamp," also figurative, from assimilated form of in- "into, in, on, upon" (see in- (2)) + premere "to press" (see press (v.1)). Literal sense of "to apply with pressure, make a permanent image in, indent, imprint" is from early 15c. in English. Related: Impressed; impressing.
impress (n.): "act of impressing" (1590s), also "characteristic mark" (1580s), from impress (v.1). From 1620s as "badge worn by nobility or their retainers," from Italian impresa; earlier in English in this sense as impreso, imprese (1580s).
impress (v.2): "levy for military service," 1590s, from assimilated form of in- (2) "into, in" + press (v.2). Related: Impressed; impressing.
impressable (adj.): "liable to be impressed into public service," 1865, from impress (v.2) + -able. Earlier it was used in the sense "capable of receiving impression" and "impressionable." Related: Impressability.
impressed (adj.): early 15c., "pressed or forced upon" (the mind), past participle adjective from impress (v.).
impressible (adj.): "capable of receiving impression," 1620s, from impress (v.1) + -able. Related: Impressibly; impressibility.
impression (n.): late 14c., "mark produced by pressure," also "image produced in the mind or emotions by something external," from Old French impression "print, stamp; a pressing on the mind" (13c.), from Latin impressionem (nominative impressio) "a pressing into, onset, attack," figuratively "a perception, mental impression," literally "a pressing into," from imprimere "press into or upon" (see impress (v.1)).

Meaning "act or process of making a mark upon the surface by pressing" is from early 15c.. Meaning "copy made by pressure from type or an engraving" is from 1550s; that of "printing of a number of copies, aggregate of copies printed at one time" is from 1570s. Meaning "belief, vague notion" (as in under the impression) is from 1610s.
impressionable (adj.): "susceptible to (mental) impressions," 1827, from French impressionable (earliest English examples are in French translations and settings); see impression + -able. Related: Impressionability (1831). Earlier was impressible (1620s).
impressionism (n.): 1839 as a term in philosophy, from impression + -ism. With reference to the French art movement, 1879, from impressionist. Extended 1880s to music (Debussy), literature, etc.
impressionist adj., n.: in reference to a style of painting aiming to represent overall impressions as they first strike the eye rather than exact details, 1876 (adjective and noun), from French, coined 1874 by French critic Louis Leroy ("école impressionniste") in a disparaging reference to Monet's sunset painting "Impression, Soleil Levant." Later extended to other arts.
impressionistic (adj.): "of or pertaining to impressionists or their work," 1883; see impressionist + -ic.
impressive (adj.): 1590s, "capable of being easily impressed" (a sense now rare or obsolete), from impress (v.1) + -ive. Meaning "capable of making an impression on the mind or senses, tending to excite attention and feeling" is from 1775. Related: Impressively; impressiveness.
impressment (n.): 1796, "act of impressing into public service or use," from impress (v.2) + -ment.
imprevisible (adj.): "that cannot be foreseen," 1855, from assimilated form of in- "not, opposite of" (see in- (1)) + previsible (see pre- + visible). Related: Imprevision; imprevisibility.
imprimatur (n.): "licence to print, granted by a licenser of the press," 1640, Modern Latin, literally "let it be printed," the formula of a book licenser, third person singular present subjunctive passive of Latin imprimere "to print, engrave, stamp; press upon, press against" (see impress (v.1)). Originally of state licence to print books, later only of Roman Catholic Church.
imprint (v.): formerly also emprint, late 14c., imprenten, emprenten, "to mark by pressure, stamp; to impress on the mind or memory," from Old French empreinter "to stamp, engrave, imprint," from empreinte "mark, impression, imprint" (13c.), noun use of fem. past participle of eimpreindre "to impress, imprint," from Vulgar Latin *impremere, from Latin imprimere "to impress, imprint" (see impress (v.1)).
imprint (n.): mid-15c., emprente "an imprint or mark, impression made by printing or stamping," from Old French empreinte "mark, impression, imprint" (see imprint (v.)). Meaning "publication information of a book" (1790) is directly from the verb.
imprison (v.): c. 1300, from Old French emprisoner "imprison; be in prison" (12c.), from assimilated form of in- "in" (see in- (2)) + prison (see prison). Formerly also emprison. Related: Imprisoned; imprisoning.
imprisonment (n.): late 14c., from Anglo-French emprisonement (13c.), Old French emprisonnement "capture, imprisonment" (13c.), from emprisoner (see imprison).
improbability (n.): 1590s, "fact or quality of being improbable;" see improbable + -ity. Meaning "an instance of something improbable" is from 1610s.
improbable (adj.): 1590s, from assimilated form of in- (1) "not, opposite of" + probable, or else from Latin improbabilis. Related: Improbably.
improbity (n.): "want of integrity," 1590s, from Latin improbitas "badness, dishonesty," from assimilated form of in- "not" (see in- (1)) + probitas "uprightness, honesty," from probus "worthy, good" (see prove).
imprompt (adj.): "not ready, unprepared," 1759, from Latin impromptus "unready, hesitating," from assimilated form of in- "not, opposite of" (see in- (1)) + promptus "ready" (see prompt (v.)).
impromptitude (n.): 1848, probably from French impromptitude, from assimilated form of in- "not, opposite of" (see in- (1)) + promptitude (see prompt (adj.)).
impromptu (adv.): 1660s, from French impromptu (1650s), from Latin in promptu "in readiness," from assimilated form of in- "into, in, on, upon" (see in- (2)) + promptu, ablative of promptus "ready, prepared; set forth, brought forward," from past participle of promere "to bring out," from pro- "before, forward, for" (see pro-) + emere "to obtain" (see exempt (adj.)). From 1764 as an adjective; as a noun from 1680s.
improper (adj.): mid-15c., "not true," from Old French impropre (14c.) and directly from Latin improprius "not proper," from assimilated form of in- "not, opposite of" (see in- (1)) + proprius (see proper). Meaning "not suited, unfit" is from 1560s; that of "not in accordance with good manners, modesty, or decency" is from 1739. Related: Improperly (late 14c.).
impropriety (n.): 1610s, "quality or fact of being improper," from French impropriété (16c.) or directly from Latin improprietas "impropriety," from improprius "improper" (see improper). As "improper thing," 1670s.
improv (n.): 1970 as colloquial shortening for improvisation. The famous New York City comedy club, founded in 1963, was, in full, The Improvisation.
improvable (adj.): 1640s, from improve (v.) + -able.
improve (v.): late 15c., "to use to one's profit, to increase (income)," from Anglo-French emprouwer "to turn to profit" (late 13c.), from Old French en-, a causative prefix or from em-, + prou "profit," from Latin prode "advantageous" (see proud (adj.)).

Spelling with -v- was rare before 17c.; it apparently arose from confusion of -v- and -u-. Spelling otherwise deformed by influence of words in -prove. Meaning "make better, raise to a better quality or condition" first recorded 1610s. Intransitive sense "get better" is from 1727. Phrase improve the occasion retains the etymological sense. Meaning "to turn land to profit" (by clearing it, erecting buildings, etc.) was in Anglo-French (13c.) and survived or was revived in the American colonies and Australia. Hence, "make good use of, occupy (a place) and convert to some purpose."
improvement (n.): mid-15c., enprowment "profitable use, management of something for profit," from Anglo-French emprowement, from emprouwer "turn to profit" (see improve). Meaning "betterment; act of making better, amelioration" is from 1640s. Meaning "production of something better, something better (than something else)" is from 1712. Meaning "buildings, etc. on a piece of property" is from 1773. Related: Improvements.
improvidence (n.): "lack of foresight, rashness," mid-15c., from Late Latin improvidentia, from assimilated form of in- "not" (see in- (1)) + Latin providentia "foresight, precaution" (see providence).
improvident (adj.): 1510s, from assimilated form of in- (1) "not, opposite of" + provident. It retains a stronger connection with the "provide" aspect of Latin providere than provident nowdoes. Related: Improvidently.
improvisation (n.): "act of improvising musically," 1786, from French improvisation, from improviser "compose or say extemporaneously" (17c.), from Italian improvisare "to sing or speak extempore," from Latin improviso "unforeseen; not studied or prepared beforehand," ablative of improvisus "not foreseen, unexpected," from assimilated form of in- "not, opposite of" (see in- (1)) + provisus "foreseen," also "provided," past participle of providere "foresee, provide" (see provide). From music the sense expanded to a general meaning "do or perform on the spur of the moment."
improvisational (adj.): 1879; see improvisation + -al (1). Earlier adjectives were improvisatorial (1819), improvisatory (1806).
improvise (v.): 1808, from Italian improvisare "to sing or speak extempore" (see improvisation), and partly from French improviser. Regarded as a foreign word and generally printed in italics in English in early 19c. Other verbs were improvisate (1825), improvisatorize (1828), the latter from improvisator "one of a class of noted extemporaneous poets of Italy" (1765), the earliest word of the group to appear in English. Related: Improvised; improvising.
The metre generally adopted for these compositions was the ottava rima, although Doni affirms that the Florentines used to improvise* in all kinds of measure.
* This new-coined verb is introduced to avoid circumlocution, for this time only: therefore I hope your readers will excuse it. I conjugate it after the regular verb to revise -- improvise -- improvising -- improvised. ["On the Improvvisatori of Italy," in "The Athenaeum," August 1808]

Our travellers have introduced among us the substantive improvisatore unaltered from the Italian; but as the verb improvisare could not be received without alteration, we lack it altogether, though the usage of the noun requires that of the verb: I here endeavor to supply the deficience by the word improvisate. [Samuel Oliver Jr., "A General, Critical Grammar of the Inglish Language," London, 1825]
improvision (n.): "want of forethought," 1640s, from assimilated form of in- (1) "not, opposite of" + provision.
imprudence (n.): early 15c., "quality of rashness or heedlessness; imprudent act," from Old French imprudence (14c.) or directly from Latin imprudentia "lack of foresight, inconsiderateness, ignorance, inadvertence," noun of quality from imprudens "unaware, inconsiderate" (see imprudent).
imprudent (adj.): late 14c., from Latin imprudentem (nominative imprudens) "not foreseeing, unaware, inconsiderate, heedless," from assimilated form of in- "not, opposite of" (see in- (1)) + prudens, contraction of providens, present participle of providere "to provide," literally "to see before (one)" (see provide). Related: Imprudently.