Like a 45-degree angle (5)
I believe the answer is:
acute
'like a 45-degree angle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acute that I've seen before include "Extremely sharp or intense" , "Keen, good or sharp, senses say" , "Angle of less than 39 degrees" , "not seen in cafe here!" , "(Of an angle) less than 90 degrees" .)