Firm can be an adjective meaning resistant, secure, or determined, or a noun meaning a business enterprise or a team of doctors. Learn the different meanings, synonyms, and usage of firm with examples and translations. Definition of firm adjective in Oxford Advanced Learner's Dictionary. Meaning , pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. The meaning of FIRM is securely or solidly fixed in place. How to use firm in a sentence. FIRM meaning : 1. not soft but not completely hard: 2. well fixed in place or position: 3. fixed at the same…. Learn more.