Full Idea
Both 30° and 60° are clearly acute angles. 'Acute' is precise in all relevant respects. Nevertheless, 30° is acuter than 60°.
Gist of Idea
A vague term can refer to very precise elements
Source
Timothy Williamson (Vagueness [1994], 4.11)
Book Reference
Williamson,Timothy: 'Vagueness' [Routledge 1996], p.126
A Reaction
A very nice example of something which is vague, despite involving precise ingredients. But then 'bald' is vague, while 'this is a hair on his head' is fairly precise.