certainly 23 synonyms and 7 antonyms for certainly, ranked by how commonly they're used. Adv — Without any doubt; definitely. Synonyms for certainly damn right damn straight fo shizzle for sure oh yeah wye aye assuredly categorically decisively doubtless ex facie for a fact for certain positively questionlessly self-evidently unarguably undeniably unconditionally undoubtably univocally without doubt without question Antonyms for certainly arguably conditionally debatably deniably doubtfully questionably uncertainly ← Back to the full definition of certainly
