Online Etymology Dictionary

secateurs (n.): pruning shears, 1881, from French sécateur, ultimately from Latin secare "to cut" (see section (n.)).
secede (v.): 1702, "to leave one's companions," from Latin secedere "go away, withdraw, separate; rebel, revolt" (see secession). Sense of "to withdraw from a political or religious alliance of union" is recorded from 1755, originally especially in reference to the Church of Scotland. Related: Seceded; seceding; seceder.
secession (n.): 1530s, from Latin secessionem (nominative secessio) "a withdrawal, separation; political withdrawal, insurrection, schism," noun of action from past participle stem of secedere "secede," from se- "apart" (see secret) + cedere "to go" (see cede). Originally in a Roman historical context, "temporary migration of plebeians from the city to compel patricians to address their grievances;" modern use in reference to religious or political unions dates from 1650s.
secessionist (n.): 1860, first recorded in U.S. context, from secession + -ist (colloquial short form secesh, noun and adjective, is attested from 1861); the earlier noun had been seceder, but this had religious overtones, especially in reference to Scottish Church history.
seclude (v.): mid-15c., "to shut up, enclose, confine," from Latin secludere "shut off, confine," from se- "apart" (see secret) + -cludere, variant of claudere "to shut" (see close (v.)). Meaning "to remove or guard from public view" is recorded from 1620s. Related: Secluded; secluding.
secluded (adj.): c. 1600, of persons; in reference to places, 1798, past participle adjective from seclude (v.). Earlier secluse (1590s).
seclusion (n.): 1610s, from Medieval Latin seclusionem (nominative seclusio), noun of action from past participle stem of Latin secludere (see seclude).
seclusive (adj.): 1743, from Latin seclus-, past participle stem of secludere (see seclude) + -ive. Related: Seclusively; seclusiveness.
Seconal: 1935, U.S. proprietary name (Eli Lilly & Co.), from Secon(dary) Al(lyl).
second (adj.): "next after first," c. 1300, from Old French second, secont, and directly from Latin secundus "following, next in time or order," also "secondary, subordinate, inferior," from root of sequi "follow" (see sequel). Replaced native other in this sense because of the ambiguousness of the earlier word. Second sight is from 1610s; an etymologically perverse term, because it means in reality the sight of events before, not after, they occur. Second fiddle first attested 1809:
A metaphor borrowed from a musical performer who plays the second or counter to one who plays the first or the "air." [Bartlett, "Dictionary of Americanisms," 1848]
second (n.1): "one-sixtieth of a minute of degree," also "sixtieth part of a minute of time," late 14c. in geometry, from Old French seconde, from Medieval Latin secunda, short for secunda pars minuta "second diminished part," the result of the second division of the hour by sixty (the first being the "prime minute," now called the minute), from Latin secunda, fem. of secundus (see second (adj.)). The second hand of a clock is attested from 1759.
second (v.): 1580s, "to support or represent in a duel, fight, etc.," from Middle French seconder, from Latin secundare "to assist, make favorable," from secundus "assisting, favorable, following, second" (see second (adj.)). The parliamentary sense is first recorded 1590s. Related: Seconded; seconding.
second (n.2): "assistant, supporter," 1580s, from second (v.).
second nature (n.): late 14c., from Latin secundum naturam "according to nature" (Augustine, Macrobius, etc.), literally "following nature;" from medieval Aristotelian philosophy, contrasted to phenomena that were super naturam ("above nature," such as God's grace), extra naturam ("outside nature"), supra naturam ("beyond nature," such as miracles), contra naturam "against nature," etc.
second-class (adj.): 1833, from noun phrase (1810), from second (adj.) + class (n.). Phrase second-class citizen is recorded from 1942.
The Negro recognizes that he is a second-class citizen and that status is fraught with violent potentialities, particularly today when he is living up to the full responsibilities of citizenship on the field of battle. [Louis E. Martin, "To Be or Not to Be a Liberal," in "The Crisis," September 1942]
second-guess (v.): 1941, back-formation from second-guesser (1937), American English, originally baseball slang for a fan who loudly questions decisions by players, managers, etc.; perhaps from guesser in the baseball slang sense of "umpire."
second-hand (adj.): also secondhand, late 15c., from second (adj.) + hand (n.).
second-rate (adj.): 1660s, originally of ships; see rate (n.).
secondary (adj.): late 14c., from Latin secundarius "pertaining to the second class, inferior," from secundus (see second (adj.)). Of colors, from 1831; of education, from 1809. Of sex characteristics from 1780. Opposed to primary or principal. Related: Secondarily.
secondly (adv.): late 14c., from second (adj.) + -ly (2).
secondment (n.): 1897, from second (v.) + -ment.
seconds (n.): "articles below the first quality," c. 1600, plural of second (n.) "that which is after the first" (early 14c.), from second (adj.); originally attested in this sense in a Shakespeare sonnet. Meaning "second helping of food at a meal" is recorded from 1792.
secrecy (n.): 1570s, from secretee, "quality of being secret" (early 15c.), from Old French secré, variant of secret (see secret (n.)) + -ty (2). Form altered on model of primacy, etc.
secret (n.): late 14c., from Latin secretus "set apart, withdrawn; hidden, concealed, private," past participle of secernere "to set apart, part, divide; exclude," from se- "without, apart," properly "on one's own" (see se-) + cernere "separate" (see crisis).

As an adjective from late 14c., from French secret, adjective use of noun. Open secret is from 1828. Secret agent first recorded 1715; secret service is from 1737; secret weapon is from 1936.
secret (v.): "to keep secret" (described in OED as "obsolete"), 1590s, from secret (n.). Related: Secreted; secreting.
secretaire (n.): cabinet for private papers, 1771, from French secrétaire (13c.), from Medieval Latin secretarius (see secretary). Englished form secretary is attested in this sense from 1803.
secretarial (adj.): 1801, from stem of secretary (Medieval Latin secretarius) + -al (1).
secretariat (n.): "office of secretary," 1811, from French secrétariat, from Medieval Latin secretariatus, from secretarius (see secretary). Meaning "division of the Central Committeee of the USSR" is from 1926, from Russian sekretariat.
secretary (n.): late 14c., "person entrusted with secrets," from Medieval Latin secretarius "clerk, notary, confidential officer, confidant," a title applied to various confidential officers, noun use of adjective meaning "private, secret, pertaining to private or secret matters" (compare Latin secretarium "a council-chamber, conclave, consistory"), from Latin secretum "a secret, a hidden thing" (see secret (n.)).

Meaning "person who keeps records, write letters, etc.," originally for a king, first recorded c. 1400. As title of ministers presiding over executive departments of state, it is from 1590s. The word also is used in both French and English to mean "a private desk," sometimes in French form secretaire. The South African secretary bird so called (1786) in reference to its crest, which, when smooth, resembles a pen stuck over the ear. Compare Late Latin silentiarius "privy councilor, 'silentiary," from Latin silentium "a being silent."
secrete (v.): 1707, back-formation from secretion. Related: Secreted; secretes; secreting.
secretion (n.): 1640s, "act of secreting;" 1732, "that which is secreted," from French sécrétion, from Latin secretionem (nominative secretio) "a dividing, separation," noun of action from past participle stem of secernere "to separate, set apart" (see secret (n.)).
secretive (adj.): "inclined to secrecy," 1815 (implied in secretiveness); see secret (n.) + -ive. The word also was in Middle English with a sense "secret, hidden" (mid-15c.). Related: Secretively.
secretly (adv.): early 15c., from secret (adj.) + -ly (2).
secretory (adj.): 1690s; see secrete + -ory.
sect (n.): mid-14c., "distinctive system of beliefs or observances; party or school within a religion," from Old French secte, sete "sect, religious community," or directly from Late Latin secta "religious group, sect in philosophy or religion," from Latin secta "manner, mode, following, school of thought," literally "a way, road, beaten path," from fem. of sectus, variant past participle of sequi "follow," from PIE *sekw- (1) "to follow" (see sequel). Confused in this sense with Latin secta, fem. past participle of secare "to cut" (see section (n.)). Meaning "separately organized religious body" is recorded from 1570s.
sectarian (adj.): 1640s, originally applied by Presbyterians to Independents, from Medieval Latin sectarius, from secta (see sect).
sectarianism (n.): 1670s, "disposition to petty sects in opposition to things established" [Johnson]; see sectarian + -ism.
sectary (n.): "member or adherent of a sect," 1550s, from French sectaire or directly from Medieval Latin sectarius, from secta (see sect).
section (n.): late 14c., "intersection of two straight lines; division of a scale;" from Old French section or directly from Latin sectionem (nominative sectio) "a cutting, cutting off, division," noun of action from past participle stem of secare "to cut," from PIE root *sek- "to cut" (source also of Old Church Slavonic seko, sešti "to cut," se čivo "ax, hatchet;" Lithuanian isekti "to engrave, carve;" Albanian šate "mattock;" Old Saxon segasna, Old English sigðe "scythe;" Old English secg "sword," seax "knife, short sword;" Old Irish doescim "I cut;" Latin saxum "rock, stone").

From 1550s as "act of cutting or dividing." Meaning "subdivision of a written work, statute, etc." is from 1570s. Meaning "a part cut off from the rest" is from early 15c.
section (v.): "divide into sections," 1819, from section (n.). Related: Sectioned; sectioning.
sectional (adj.): 1806; see section (n.) + -al (1). Noun meaning "piece of furniture composed of sections which can be used separately" is attested by 1961, from sectional seat, sectional sofa, etc. (1949).
sectionalism (n.): 1836, American English, from sectional + -ism. In frequent use from 1856.
sector (n.): 1560s, "section of a circle between two radii," from Late Latin sector "section of a circle," in classical Latin "a cutter, one who cuts," from sectus, past participle of secare "to cut" (see section (n.)). Translated Greek tomeus in Latin editions of Archimedes. Meaning "area, division" appeared 1920, generalized from military sense (1916) of "part of a front," based on a circle centered on a headquarters. As a verb from 1884. Related: Sectoral; sectorial.
secular (adj.): c. 1300, "living in the world, not belonging to a religious order," also "belonging to the state," from Old French seculer (Modern French séculier), from Late Latin saecularis "worldly, secular, pertaining to a generation or age," from Latin saecularis "of an age, occurring once in an age," from saeculum "age, span of time, generation."

According to Watkins, this is probably from PIE *sai-tlo-, with instrumental element *-tlo- + *sai- "to bind, tie" (see sinew), extended metaphorically to successive human generations as links in the chain of life. Another theory connects it with words for "seed," from PIE root *se- "to sow" (see sow (v.), and compare Gothic mana-seþs "mankind, world," literally "seed of men").

Used in ecclesiastical writing like Greek aion "of this world" (see cosmos). It is source of French siècle. Ancient Roman ludi saeculares was a three-day, day-and-night celebration coming once in an "age" (120 years). In English, in reference to humanism and the exclusion of belief in God from matters of ethics and morality, from 1850s.
secularism (n.): "doctrine that morality should be based on the well-being of man in the present life, without regard to religious belief or a hereafter," 1846, from secular + -ism.
secularist (n.): 1846, "one who theoretically rejects and ignores all forms of religion based on revelation;" see secularism + -ist. From 1851 as "one who maintains that public education and civil policy should be conducted without the introduction of a religious element." Related: Secularistic.
secularization (n.): 1706, "conversion to secular purposes," in reference to Church property; see secularize + -ation. General use by 1863.
secularize (v.): 1610s, of property, offices, etc., from secular + -ize. From 1711 as "to become worldly;" from 1846 of education, social institutions, etc. Related: Secularized; secularizing.
secundine (n.): "afterbirth," from Late Latin secundinae (plural), from Latin secundae "the afterbirth," shortened from secundae membranae, literally "the second membranes," from secundus "second" (see second (adj.)). Related: Secundines.
secure (adj.): 1530s, "without care, dreading no evil," from Latin securus, of persons, "free from care, quiet, easy," also in a bad sense, "careless, reckless;" of things, "tranquil; free from danger, safe," from *se cura, from se "free from" (see secret (n.1)) + cura "care" (see cure (n.)).

In English, of places, "free from danger, unexposed," from 1580s. Meaning "firmly fixed" (of material things) is from 1841, on notion of "affording grounds for confidence." Of telephones, "not wiretapped," from 1961. Replaced Middle English siker, from Old English sicor, from the Latin word. Related: Securely.