mid-14c., pokete, "bag, pouch, small sack," from Anglo-French pokete (13c.), diminutive of Old North French poque "bag" (Old French pouche), from a Germanic source akin to Frankish *pokka "bag," from Proto-Germanic *puk- (see poke (n.)).
Meaning "small bag worn on the person, especially one sewn into a garment" is from early 15c. Sense in billiards is from 1754. Mining sense is attested from 1850; military sense of "area held by troops surrounded by the enemy" is from 1918; the general sense of "small area different than its surroundings" (1926) apparently was extended from the military use. Figuratively, "one's money" (conceived as being kept in a pocket) is from 1717. Pope Pokett (late 15c.) was figurative of the greedy and corrupt Church.
1580s, "to place in a pocket" (often with implications of dishonesty), from pocket (n.). From the earliest use often figurative. Meaning "to form pockets" is from c.1600. Related: Pocketed; pocketing.
1610s, "of or pertaining to or meant for a pocket," from pocket (n.). Pocket-knife is first recorded 1727; pocket-money is attested from 1630s. Often merely implying a small-sized version of something, e.g. of warships, from 1930, and cf. Pocket Venus "beautiful, small woman," attested from 1808. Pocket veto attested from 1842, American English.
The "pocket veto" can operate only in the case of bills sent to the President within ten days of Congressional adjournment. If he retain such a bill (figuratively, in his pocket) neither giving it his sanction by signing it, nor withholding his sanction in returning it to Congress, the bill is defeated. The President is not bound to give reasons for defeating a bill by a pocket veto which he has not had at least ten days to consider. In a regular veto he is bound to give such reasons. [James Albert Woodburn, "The American Republic and its Government," Putnam's, 1903]
pocket pock·et (pŏk'ĭt)
In anatomy, a cul-de-sac or pouchlike cavity.
A diseased space between the inflamed gum and the surface of a tooth.
A collection of pus in a nearly closed sac.
To enclose within a confined space.
To approach the surface at a localized spot, as with the thinned out wall of an abscess which is about to rupture.
Absent or otherwise unavailable: I'm out of the pocket for a bit, but I'll get back at ya (1974+)