picklock n.

early 13c., picken "to peck;" c. 1300, piken "to work with a pick, to dig up," probably representing a fusion of Old English *pician "to prick," (implied by picung "a piercing, pricking," an 8c. gloss on Latin stigmata) with Old Norse pikka "to prick, peck," both from a Germanic root (source also of Middle Dutch picken, German picken "to pick, peck"), perhaps imitative. Influence from Middle French piquer "to prick, sting" (see pike (n.1)) also is possible, but that French word generally is not considered a source of the English word. Related: Picked; picking.

Meaning "to pluck with the hand or fingers, gather, break off, collect" (fruit, etc.) is from early 14c.; that of "to prick or pierce with a pointed instrument" also is from early 14c. The meaning "to choose, sort through carefully in search of valuable material" emerged late 14c., from the earlier meaning "to pluck with the fingers." The sense of "to rob, plunder" (c. 1300) weakened to a milder sense of "steal petty things, filch or pilfer from" by late 14c.  Meaning "to eat with small bites" is from 1580s.

Of locks, etc., "probe or penetrate with a pointed tool," early 15c. The meaning "to pluck (a banjo, etc.) with the fingers" is recorded from 1860. To pick a quarrel, fight, etc. is from mid-15c.; to pick at "annoy with repeated fault-finding" is from 1670s. To pick on "single out for adverse attention" is from late 14c. Also see pick up.

To pick off "shoot one by one" is recorded from 1810; baseball sense, of a pitcher or catcher, "to put out a runner caught off base" is by 1939. To pick and choose "select carefully" is from 1660s (choose and pick is attested from c. 1400). To pick (one's) nose is by mid-15c.

"means of fastening," Old English loc "bolt, appliance for fastening a door, lid, etc.; barrier, enclosure; bargain, agreement, settlement, conclusion," from Proto-Germanic *lukana-, a verbal root meaning "to close" (source also of Old Frisian lok "enclosure, prison, concealed place," Old Norse lok "fastening, lock," Gothic usluks "opening," Old High German loh "dungeon," German Loch "opening, hole," Dutch luik "shutter, trapdoor").

Ordinary mechanical locks work by means of an internal bolt or bar which slides and catches in an opening made to receive it. "The great diversity of meaning in the Teut. words seems to indicate two or more independent but formally identical substantival formations from the root" [OED]. The Old English sense "barrier, enclosure" led to the specific meaning "barrier on a stream or canal" (c. 1300), and the more specific sense "gate and sluice system on a water channel used as a means of raising and lowering boats" (1570s).

From 1540s as "a fastening together," hence "a grappling in wrestling" (c. 1600). In firearms, the part of the mechanism which explodes the charge (1540s, probably so called for its resemblance to a door-latching device), hence figurative phrase lock, stock, and barrel (which add up to the whole firearm) "the whole of something" (1842). Phrase under lock and key attested from early 14c.