Colloquial language is casual and conversational: it's the difference between "What are you going to do?" and "Whatchagonnado?" Define colloquial . colloquial synonyms, colloquial pronunciation, colloquial translation, English dictionary definition of colloquial . not formal or literary; belonging to or typical of ordinary or familiar language Not to be confused with: colloquium – an academic conference or seminar... Definition of colloquial adjective in Oxford Advanced Learner's Dictionary. Meaning , pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. 2 meanings: 1. of or relating to conversation 2. denoting or characterized by informal or conversational idiom or vocabulary →.... Click for more definitions.