The phenomenon, where a single word is associated with two or several related meanings, is known as—

Polysemy refers to the phenomenon where a single word has multiple related meanings (e.g., 'mouth' meaning the body part and the mouth of a river). Homonyms are words with the same form but unrelated meanings. Homographs are words spelled the same but possibly with different pronunciations and meanings. The key distinguishing feature in the question is 'related meanings', which precisely defines polysemy. Hence (3) is correct.