Knuc″kle, v. i. [imp. & p. p.Knuckled (?);; p. pr. & vb. n.Knuckling (?).] To yield; to submit; — used with down, to, or under.
To knuckle to. (a) To submit to in a contest; to yield to. See To knock under, under Knock, v. i. (b) To apply one's self vigorously or earnestly to; as, to knuckle to work.