The antonyms for the word "declare lawful" are plentiful and varied. Words like prohibit, outlaw, ban, and illegalize all convey the opposite meaning of allowing or permitting something. Similarly, terms like disapprove, condemn, forbid, and denounce all indicate a rejection or condemnation of the legality of something. Other antonyms might include terms like invalidate, annul, nullify, and cancel, which suggest a negation or revocation of a previously declared lawfulness. Ultimately, the antonyms for "declare lawful" all point towards the opposite concept of making something allowable or legitimate, highlighting the importance of language and semantics in shaping our understanding of the world around us.