Is there a name for a pair of words or phrase that can have a double meaning? [closed]

A word or phrase that has more than one related meaning or sense is a polyseme. You can read a fairly good overview of polysemy here.

However, your examples are somewhat different from those on the link I've provided. Your examples are, more specifically, about the potential confusion caused when we assemble two or more nouns into phrases. The relationship between those nouns can become unclear, though context usually works it out.

Double entendre might be what you're looking for. A double entendre is a phrase meant to mean two things. Double entendre can imply there's an innocent meaning and a dirty meaning, but you could still use it for "werewolf hunter," especially if you put it in a sentence where the whole sentence made sense with either meaning. http://en.wikipedia.org/wiki/Double_entendre

If you're looking for something a bit less specific, you could just say it is an ambiguous phrase.