What kind of word is "squeak"?

The word squeak is several kinds of word depending on use. Primarily, squeak is a noun and a verb, and it is also an onomatopoeia, which is a word that imitates the sound it describes. As a noun, squeak is a common, countable, concrete noun meaning a short high-pitched sound, as in I heard a squeak. As a verb, squeak is a regular, intransitive and sometimes transitive verb meaning to make a squeak, as in the door squeaks, with forms squeaks, squeaking, squeaked. As onomatopoeia, squeak is an imitative word where pronunciation sounds like the noise itself, similar to buzz, hiss, and pop. Grammatically, squeak can also be part of adjective squeaky and adverb squeakily. In linguistics, it is a CVC structure with initial consonant cluster. In slang, squeak can be verb meaning to inform. So kind of word is onomatopoeic noun and verb, also called sound word or echoic word. It is not a function word like preposition, it is content word carrying meaning. It is informal and descriptive, often used in children's language and everyday speech.