Word parts most + -ly Pronunciation (UK) IPA (key): /ˈməʊstli/ (US) IPA (key): /ˈmoʊstli/ Audio (US)(file) Adverb Positive mostly Comparative none Superlative none If something is mostly true, empty, sunny, etc., it is close to 100% so. Synonyms: mainly and largely Antonym: completely The cup was mostly empty. Mostly, it should be sunny today. Related words most Wikiwand - on Seamless Wikipedia browsing. On steroids.