Word parts certain + -ly Pronunciation (US) IPA (key): /ˈsɝtn̩li/ (UK) IPA (key): /ˈsɜːtn̩li/ Audio (US)(file) Adverb Positive certainly Comparative more certainly Superlative most certainly (sentence adverb) Without doubt, bound to occur. (of propositions) Used to agree with something, yes. Would you like to come with me? – Certainly. Wikiwand - on Seamless Wikipedia browsing. On steroids.