"binding in law or conscience, imposing duty, requiring performance of or forbearance from some act," c. 1400, obligatorie, from Old French obligatoire "creating an obligation, obligatory," and directly from Late Latin obligatorius "binding," from obligat-, past-participle stem of obligare "to bind, bind up, bandage," figuratively "put under obligation" (see oblige).
"writ from a superior court to an inferior court or officer specifying that something be done by the persons addressed, as being within their office or duty," 1530s (late 14c. in Anglo-French), from Latin mandamus "we order" (opening word of the writ), first person plural present indicative of mandare "to order" (see mandate (n.)). "Its use is generally confined to cases of complaint by some person having an interest in the performance of a public duty, when effectual relief against its neglect cannot be had in the course of an ordinary action" [Century Dictionary].
"of, pertaining to, or characterized by selection;" hence "using that which is choice," 1620s; see select (adj.) + -ive. Related: Selectively; selectivity; selectiveness. Selective service as a military drafting system is from 1917, American English; hence selectee "person chosen for military duty" (by 1940).
"to perform the duty of a priest," 1630s, from Medieval Latin officiatus, present participle of officiare "perform religious services," from Latin officium "a service" (in Medieval Latin, "church service"); see office. The earlier verb in English was simply office (mid-15c.). Related: Officiated; officiating.
"unwilling, strtuggling against duty or a command," 1660s, from Latin reluctantem (nominative reluctans), present participle of reluctari "to struggle against, resist, make opposition," from re- "against" (see re-) + luctari "to struggle, wrestle" (see reluctance). Related: Reluctantly. The Latin word also is the source of Spanish reluchante, Italian riluttante.
Reluctant, literally, struggling back from, implies some degree of struggle either with others who are inciting us on, or between our own inclination and some strong motive, as sense of duty, whether it operates as an impelling or as a restraining influence. [Century Dictionary]
mid-13c., "solemn pledge, promise," usually concerning a serious matter and involving risk or loss in default, from Old English pliht "danger, risk, peril, damage," from Proto-Germanic *pleg- (source also of Old Frisian plicht "danger, concern, care," Middle Dutch, Dutch plicht "obligation, duty," Old High German pfliht, German Pflicht "obligation, duty," which is perhaps from PIE root *dlegh- "to engage oneself, be or become fixed," or it might be a substratum word. Compare Old English plihtere "look-out man at the prow of a ship," plihtlic "perilous, dangerous."