1640s, "act of struggling against;" 1660s, "unwillingness, aversion;" from the obsolete verb reluct "to strive, struggle, or rebel against" (15c.), from Latin reluctari, reluctare "to struggle against, resist, make opposition," from re- "back, against, in opposition" (see re-) + luctari "to struggle, wrestle," from Proto-Italic *lukto-, from PIE *lug-to- "bent" (source also of Old Irish foloing "supports," inloing "connects;" Middle Welsh ellwng- "to set free;" Greek lygos "withy, pliant twig," lygizein "to bend, twist;" Gothic galukan "to shut," uslukan "to open;" Old English locc "twist of hair."

Related: Reluctancy (1620s.); Bacon (1605) has reluctation.

1630s, "to be locked together," from inter- "between" + lock (v.). Related: Interlocked; interlocking. As a noun, attested by 1856.

also land-locked, "almost shut in by land," 1620s, from land (n.) + past participle of lock (v.).

1832, from lock (v.) + -able. Related: Lockability.

also lock-down, from late 19c. in various mechanical senses, from the verbal phrase; see lock (v.) + down (adv.). Prison sense is by 1975, American English.

"small chest that can be locked," late 14c., agent noun from Middle English lokken (see lock (v.)). Especially for individual use in companies of men, as on shipboard or in military regiments. As a characteristic of high school life, 20c. Earlier the word meant "a mechanism for locking" (early 14c.).

also lockjaw, 1786, earlier locked-jaw (1765), popular name for trismus, also applied to tetanus, from lock (v.) + jaw (n.).

also lock-out, "act of excluding from a place by locking it up," especially of management locking out workers in labor disputes (1854) but also in 19c. the exclusion of a teacher from the schoolhouse by his pupils as an act of protest. From the verbal phrase lock (someone) out, which is attested from mid-14c. in the sense "turn or keep out (of a place), bar the doors against" (see lock (v.) + out (adv.)).

also lockup, "detention cell for offenders," 1838, perhaps short for earlier lock-up house; from the verbal phrase. Meaning "action of locking up" is from 1845. The verbal phrase lock (someone) up in a dwelling, prison, etc., is from early 15c. Of things, "to hold in safekeeping or concealment," also early 15c. See lock (v.) + up (adv.). To lock up (intransitive) "lock all the doors" (of a house, shop, etc.) is from 1901.

c. 1400, from un- (2) "reverse, opposite of" + lock (v.). Figurative sense is attested from 1530s. Old English had unlucan "to unlock, open." Related: Unlocked; unlocking.