Balanus is a biological term that refers to a genus of small, barnacle-like marine crustaceans. Synonyms for the word balanus include acorn barnacle, rock barnacle, and goose-neck barnacle. These synonyms are commonly used to describe the hardened exoskeleton of the animal which is shaped like an acorn, often found attached to rocks or other substrates in shallow or deep water. Other synonyms of balanus include sessile barnacles, cirripedes, and lepas, which are also used to describe different species of barnacles. Overall, these synonyms provide a useful vocabulary for describing the various characteristics and features of these fascinating marine animals.