From Middle English withsitten (“to resist”), from with- (“against”) + sitten (“to be positioned, sit”). More at with-, sit.
withsit (third-person singular simple present withsits, present participle withsitting, simple past withsat, past participle withsat or withsitten)
- (archaic, transitive) To resist, oppose, be set against or in opposition to.
- (archaic, transitive) To withstand.