Online Etymology Dictionary

unsubstantial (adj.): mid-15c., from un- (1) "not" + substantial (adj.).
unsubstantiated (adj.): 1775, from un- (1) "not" + past participle of substantiate (v.).
unsuccessful (adj.): 1610s, from un- (1) "not" + successful (adj.). Related: Unsuccessfully. A noun unsuccess "lack of success" is recorded from 1580s.
unsuitable (adj.): 1590s, from un- (1) "not" + suitable (adj.). Related: Unsuitably; unsuitability.
unsuited (adj.): "unfit," 1590s, from un- (1) "not" + past participle of suit (v.).
unsullied (adj.): 1580s, from un- (1) "not" + past participle of sully (v.).
unsung (adj.): early 15c., "not uttered in a song," from un- (1) "not" + past participle of sing (v.). Similar formation in German ungesungen. Meaning "not celebrated" is recorded from 1660s.
unsupervised (adj.): 1845, from un- (1) "not" + past participle of supervise (v.).
unsupported (adj.): early 15c., from un- (1) "not" + past participle of support (v.).
unsure (adj.): c. 1400, "not safe against attack," also "lacking certainty," from un- (1) "not" + sure (adj.).
unsurmountable (adj.): "incapable of being overcome," 1701, from un- (1) "not" + surmountable.
unsurpassable (adj.): 1610s, from un- (1) "not" + surpassable (see surpass (v.)).
unsurpassed (adj.): 1775, from un- (1) "not" + past participle of surpass (v.).
unsuspected (adj.): 1520s, from un- (1) "not" + past participle of suspect (v.).
unsuspecting (adj.): 1590s, from un- (1) "not" + present participle of suspect (v.).
unsustainable (adj.): 1670s, from un- (1) "not" + sustainable (adj.).
unswayed (adj.): 1590s, from un- (1) "not" + past participle of sway (v.).
unsweetened (n.): 1775, "not having been sweetened," from un- (1) "not" + past participle of sweeten (v.); or else, if the sense is "with sweetness removed," from unsweeten (v.), which is attested from 1610s.
unswerving (adj.): 1690s, from un- (1) "not" + present participle of swerve (v.).
unsympathetic (adj.): 1785, from un- (1) "not" + sympathetic (adj.).
unsystematic (adj.): 1770, from un- (1) "not" + systematic (adj.).
untainted (adj.): 1580s, in the moral sense; c. 1600 in the physical sense; from un- (1) "not" + past participle of taint (v.). Earlier was untained (mid-15c.), from a Middle English variant of taint (v.).
untamed (adj.): mid-14c., from un- (1) "not" + past participle of tame (v.). Similar formation in Old English untemed, Old Norse utamdr, Old High German ungizamot.
untangible (adj.): 1775, from un- (1) "not" + tangible (adj.).
untangle (v.): 1540s, from un- (2) "reverse, opposite of" + tangle (v.). Related: Untangled; untangling.
untapped (adj.): 1775, from un- (1) "not" + past participle of tap (v.). Figurative use from c. 1890.
untaught (adj.): mid-14c., "not instructed or educated," from un- (1) "not" + taught. Hence "spontaneous, natural" (mid-15c.).
untempered (adj.): mid-15c., "not properly mixed, undiluted," from un- (1) "not" + past participle of temper (v.). Similar formation in Middle Dutch ongetempert, Middle High German ungetempert. Earlier as "unrestrained" (late 14c.), also, of a musical instrument, "not properly tuned;" meaning "unhardened" is from 1820.
untenable (adj.): 1640s, "indefensible, incapable of being held against attack," from un- (1) "not" + tenable (adj.). Figurative sense is recorded from 1690s.
untenanted (adj.): 1670s, from un- (1) "not" + tenanted (see tenant (n.)).
untether (v.): 1775, from un- (2) "reverse, opposite of" + tether (v.). Related: Untethered; untethering.
untethered (adj.): 1775, past participle adjective from untether (v.).
unthaw (v.): 1590s, "to thaw," from un- (2) "opposite of" + thaw (v.). Related: Unthawed; unthawing. Unthawed also sometimes is used with a sense "frozen" (1610s.).
unthinkable (adj.): early 15c., "too large to be conceived, unimaginable," from un- (1) "not" + think (v.) + -able. Meaning "incapable of being framed by thought" is recorded from mid-15c.
unthinking (adj.): 1670s, "unreflecting;" 1680s, "heedless," from un- (1) "not" + present participle of think (v.).
unthrifty (adj.): late 14c., "unprofitable, useless," from un- (1) "not" + thrifty (adj.), or else from Middle English noun unthrift "profligacy," late 14c., earlier "evil practice, wicked act" (c. 1300).
untidy (adj.): early 13c., "untimely, unseasonable, unsuitable," from un- (1) "not" + tidy (adj.). Similar formation in West Frisian ontidich, Middle Dutch ontidich, Dutch ontijdig, Old High German unzitich, German unzeitig, Norwegian utidig "untimely, unseasonable, unfavorable." Meaning "poorly cared for, not neat" is recorded from mid-14c.
untidy (v.): "make untidy," 1891, from untidy (adj.). Related: Untidied; untidying.
untie (v.): Old English untigan "loosen, unchain," from un- (2) "opposite of" + tie (v.). Related: Untied; untying.
until (prep.): c. 1200, from till (prep.). The first element is un- "as far as, up to" (also in unto), from Old Norse *und "as far as, up to," from Proto-Germanic *und- (source also of Old English oð "up to, as far as," Old Frisian, Old Saxon, Gothic und), from PIE *nti-, from root *ant- "front, forehead" (see ante).

The two syllables have the same meaning. Originally also used of persons and places. As a conjunction from c. 1300. Similar formation in Swedish intill, Danish indtil (northern English and Scottish formerly also had intill/intil "into, in"). The Modern German equivalent, bis (Old High German biaz), is a similar compound, of Old High German bi "by, at, to" and zu "to."
untilled (adj.): late 13c., from un- (1) "not" + past participle of till (v.).
untimely (adj.): 1530s, "coming before the proper or usual time," from un- (1) "not" + timely (adj.). Similar formation in Middle Danish utimelig, of weather, etc. Old English had untidlic "unseasonable." Related: Untimeliness.
untitled (adj.): 1610s, "unnamed," from un- (1) "not" + past participle of title (v.). Meaning "having no right" is from 1660s; that of "undistinguished by an aristocratic title" is from 1798.
unto (prep.): mid-13c., perhaps a modification of until, with southern to in place of northern equivalent till. Or perhaps a contraction of native *und to, formed on the model of until from Old English *un- "up to, as far as," cognate of the first element in until. "Very rare in standard writers of the 18th c.," according to OED, and since then chiefly in dignified, archaic, or Biblical styles.
untold (adj.): Old English unteald, "not counted or reckoned," from un- (1) "not" + past participle of tell (v.) in its original numerical sense. Similar formation in Middle Dutch ongetellet, German ungezahlt, Old Norse utaliðr. Meaning "not related or recounted" is recorded from late 14c.
untouchable (adj.): 1560s, "immaterial," from un- (1) "not" + touchable (see touch (v.)). Meaning "that legally cannot be interfered with" is recorded from 1734. Meaning "too loathsome or defiling to be touched" is recorded from 1873. The noun, in reference to a hereditary low caste of India, is attested from 1909; the term and the restrictions were made illegal in India in 1947.
untouched (adj.): late 14c., "not been physically contacted," from un- (1) "not" + past participle of touch (v.). Meaning "unharmed, uninjured" is from c. 1400; that of "not used at all" is from 1530s; sense of "unmoved emotionally" is from 1610s.
untoward (adj.): 1520s, "not having inclination" (to or for something), also "difficult to manage, unruly," from un- (1) "not" + toward (adj.).
untrained (adj.): 1540s, from un- (1) "not" + past participle of train (v.).
untrammeled (adj.): also untrammelled, 1795, from un- (1) "not" + past participle of trammel (v.).