Third person singular present tense: he, she, or it renounces or solemnly swears against something.
From 'forswear' + '-s' (third person singular marker). Standard present tense conjugation of the verb 'forswear.'
This simple conjugation is how we know 'forswear' was active enough in English to get regular verb conjugations—if a word disappears, it often stops declining in normal ways first.
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