1. familiar by-form of the name ‘John’; hence a generic proper name for any man of the common people; proverb “Jack shall have Jill” MND. III. ii. 461; so LLL. V. ii. 883; in Shr. IV. i. 51 a quibble is intended (see sense 7).
2. low-bred or ill-mannered fellow, ‘knave’ Mer.V. III. iv. 77 “bragging J-s,” Shr. II. i. 159, 282  “a swearing ,” 1H4 III. iii. 98 “the prince is a , a sneak-cup,” R3 I. iii. 53, 72 “Since every became a gentleman,” Rom. II. iv. 161, III. i. 12, Ant. III. xi. [xiii.] 93, 103; see also sense 8
4. figure of a man which strikes the bell on the outside of a clock R3 IV. ii. 113, Tim. III. vi. 118.
5. in the virginal, an upright piece of wood fixed to the key-lever and fitted with a quill which plucked the string as the jack rose when the key was pressed down Sonn. cxxviii. 5 “How oft . . . Do I envy those j-s that nimble leap To kiss the tender inward of thy hand,” 13; usu. explained here as=key.
6. in bowls, a smaller bowl placed as a mark to aim at Cym. II. i. 2.
7. measure for drink, 1/4 pint Shr. IV. i. 51 “Be the J-s fair within, the Jills fair without” (cf. 1).