Language scholars use the word monosemy for a word that has only one meaning. A word like "lucrative" (producing a profit) has only one meaning, and is therefore an example of monosemy. A word like "check" is a whole other story.
When a word has just one meaning, it's completely clear and unambiguous. English is full instead of polysemy, when words have more than one meaning — like book, which means both "pages bound together" and "to arrest." The word aunt, on the other hand, only means "the sister of your mother or father," and is an example of monosemy. The Greek roots are mono, "one," and sēma, "sign."