Swear  —v. (past swore; past part. Sworn) 1 a (often foll. By to + infin. Or that + clause) state or promise solemnly or on oath. B (cause to) take (an oath) (swore them to secrecy). 2 colloq. Insist (swore he was fit). 3 (often foll. By at) use profane or obscene language. 4 (foll. By by) a appeal to as a witness in taking an oath (swear by almighty god). B colloq. Have great confidence in (swears by yoga). 5 (foll. By to; usu. In neg.) Say certainly (could not swear to it). —n. Spell of swearing.  swear blind colloq. Affirm emphatically. Swear in induct into office etc. With an oath. Swear off colloq. Promise to abstain from (drink etc.). [old english]