—Synonyms 1. Firm, hard, solid, stiff are applied to substances that tend to retain their form unaltered in spite of pressure or force. Firm often implies that something has been brought from a yielding state to a fixed or elastic one: An increased amount of pectin makes jellies firm. Hard is applied to substances so resistant that it is difficult to make any impression upon their surface or to penetrate their interior: as hard as a stone. Solid is applied to substances that without external support retain their form and resist pressure: Water in the form of ice is solid. It sometimes denotes the opposite of hollow: a solid block of marble. Stiff implies rigidity that resists a bending force: as stiff as a poker. 2. fast, stable, immovable. 4. established, confirmed. 5. determined, immovable, staunch, reliable.

—Antonyms 1. yielding, soft.