An appropriate word suits the purpose, audience, and situation. A word is a representation. A good word is as specific as possible. Words can be concrete or abstract. Words can have connotative as well as denotative value.
Words can have symbolic meaning.
Words can act as allusions. Words can act as dialect markers and language users have different oral and written vocabularies. Context influences a word's meanings. Different words have different meanings depending on the context. Language has sound patterns including rhyme, rhythm, alliteration, repetition.