A word with a wide range of meanings

Solution 1:

Polysemy - "a diversity of meanings"

A word is polysemous if it has a diversity of meanings.

Solution 2:

If a word is used in a sentence and the meaning of that word in that sentence is not obvious, I would say the sentence is ambiguous, rather than saying the word is ambiguous. For example, "I overlooked the valley." (Did you look at it, or completely miss noticing it?) or "Man was here first" (Was a man here before a woman, or was mankind here before an animal?)

A word is polysemous if it has multiple meanings, but that often doesn't mean ambiguous -- it is almost always easy to determine the meaning of a word from its context.