Webster's Revised Unabridged Dictionary · 1913

Forswear

Forswear , transitive verb

[Old English forsweren, forswerien, Anglo-Saxon forswerian; pref. for- + swerian to swear. See For-, and Swear, v. i.]

1.
To reject or renounce upon oath; hence, to renounce earnestly, determinedly, or with protestations.
I... do forswear her. — Shakespeare
2.
To deny upon oath.
Like innocence, and as serenely bold As truth, how loudly he forswears thy gold! — Dryden
Collocations (1)
To forswear one's self , to swear falsely; to perjure one's self. Thou shalt not forswear thyself. — Matt. v. 33

Forswear , intransitive verb

To swear falsely; to commit perjury. — Shakespeare