c. 1600, "that must be attended, followed, or kept," also "worthy of notice or mention," from Latin observabilis "remarkable, observable," from observare "watch over, note, heed, look to, attend to, guard, regard, comply with," from ob "in front of, before" (see ob-) + servare "to watch, keep safe," from PIE root *ser- (1) "to protect." From 1640s as "perceptible, capable of being observed." Related: Observably; observability.
From 1620s as "body of persons, appointed or elected, to whom some special business or function has been entrusted;" a new formation or else an extended sense of the old noun. Related: Committeeman; committeeship.
late 14c., observacioun, "the performance of a religious rite," from Old French observation (c. 1200) and directly from Latin observationem (nominative observatio) "a watching over, observance, investigation," noun of action from past-participle stem of observare "watch over, note, heed, look to, attend to, guard, regard, comply with," from ob "in front of, before" (see ob-) + servare "to watch, keep safe," from PIE root *ser- (1) "to protect." Sense of "act or fact of paying attention" is from 1550s. Meaning "a remark in reference to something observed" is recorded from 1590s.
"accompanying, conjoined with, concurrent, going together," c. 1600, from French concomitant, from Late Latin concomitantem (nominative concomitans), present participle of concomitari "accompany, attend," from assimilated form of com "with, together" (see con-) + comitari "join as a companion," from comes (genitive comitis) "companion," "companion, attendant," the Roman term for a provincial governor, from com "with" (see com-) + stem of ire "to go" (from PIE root *ei- "to go"). Related: Concomitantly; concomitance (1530s).
Meaning "professed lover, one devoted to the service of a lady" is from mid-14c. In North American colonies and U.S., the usual designation for "slave" 17c.-18c. (in 14c.-15c. and later in Biblical translations the word often was used to render Latin servus, Greek doulos "slave"). Public servant is attested from 1670s.
mid-15c., "consequence of an event or action, a corollary; that which follows and forms a continuation," from Old French sequelle, sequele (14c.) and directly from Late Latin sequela "that which follows, result, consequence," from sequi "to follow, come after, follow after, attend, follow naturally" (from PIE root *sekw- (1) "to follow").
Specifically "a story that follows and continues another" by 1510s.
Also in Middle English "offspring, issue descendants;" also "train of followers, retinue." Beerbohm uses sequelula "a small sequel" (1912).
c. 1300, sute, also suete, suite, seute, "a band of followers; a retinue, company;" also "set of matching garments" worn by such persons, "matching livery or uniform;" hence " kind, sort; the same kind, a match;" also "pursuit, chase," and in law, "obligation (of a tenant) to attend court; attendance at court," from Anglo-French suit, siwete, from Old French suite, sieute "pursuit, act of following, hunt; retinue; assembly" (12c., Modern French suite), from Vulgar Latin *sequita, fem. of *sequitus, from Latin secutus, past participle of sequi "to attend, follow" (from PIE root *sekw- (1) "to follow").
Legal sense of "lawsuit; legal action" is from mid-14c. Meaning "the wooing of a woman" is from late 15c. Meaning "set of clothes to be worn together" is attested from late 14c., also "matching material or fabric," from notion of the livery or uniform of court attendants. As a derisive term for "businessman," it dates from 1979. Meaning "matched set of objects, number of objects of the same kind or pattern used together" is from late 14c., as is that of "row, series, sequence." Meaning "set of playing cards bearing the same symbol" is attested from 1520s, also ultimately from the notion of livery. To follow suit (1670s) is from card-playing: "play a card of the same suit first played," hence, figuratively, "continue the conduct of a predecessor."
"obstinate in refusal," 1610s, from Latin recusantem (nominative recusans) "refusing to obey," present participle of recusare "make an objection against; decline, refuse, reject; be reluctant to" (see recuse).
Earlier as a noun in English history, specifically of those who refused to attend divine service in Anglican churches (1550s), a punishable offense, enforcement of which fell heavily on Roman Catholics. The original use of the adjective also is in reference to this.