to knock under

Webster's Dictionary (GCIDE)

Knock \Knock\ (n[o^]k), v. i. [imp. & p. p. Knocked (n[o^]kt); p. pr. & vb. n. Knocking.] [OE. knoken, AS. cnocian, cnucian; prob. of imitative origin; cf. Sw. knacka. Cf. Knack.]

1.To drive or be driven against something; to strike against something; to clash; as, one heavy body knocks against another. --Bacon. [1913 Webster]

2.To strike or beat with something hard or heavy; to rap; as, to knock with a club; to knock on the door. [1913 Webster]

For harbor at a thousand doors they knocked.— Dryden.[1913 Webster]

Seek, and ye shall find; knock, and it shall be opened unto you.— Matt. vii. 7.[1913 Webster]

3.To practice evil speaking or fault-finding; to criticize habitually or captiously. [Slang, U. S.] [Webster 1913 Suppl.]

To knock about, to go about, taking knocks or rough usage; to wander about; to saunter. [Colloq.] "Knocking about town." --W. Irving.

To knock up, to fail of strength; to become wearied or worn out, as with labor; to give out. "The horses were beginning to knock up under the fatigue of such severe service." --De Quincey.

To knock off, to cease, as from work; to desist.

To knock under, to yield; to submit; to acknowledge one's self conquered; -- an expression probably borrowed from the practice of knocking under the table with the knuckles, when conquered. "Colonel Esmond knocked under to his fate." --Thackeray. [1913 Webster]