The term 'BIG SIMIAN' is composed of two words, 'BIG' and 'SIMIAN'. The first word, 'BIG', is an adjective that means large or of considerable size. The second word, 'SIMIAN', is a noun that refers to a type of primate, such as an APE or monkey. The crossword solution for the term 'BIG SIMIAN' is 'APE', which is a three-letter word that refers to a type of primate that is characterized by its long arms, curved fingers, and tailless body.