Wiktionary
acute triangle
n. (context geometry English) A triangle all of the angles of which are acute.
WordNet
acute triangle
n. a triangle whose interior angles are all acute [syn: acute-angled triangle]
Usage examples of "acute triangle".
Each took the form of an acute triangle that had been rounded off at the top.
It appears to widen into a narrow fan, an acute triangle of red light whose base encompasses all of Y.