Sharp or intense (5)
I believe the answer is:
acute
I believe this clue is a double definition.
'sharp' is the first definition.
(I know that sharp can be written as acute)
'intense' is the second definition.
(synonyms)
(Other definitions for acute that I've seen before include "Piercing" , "Short and severe" , "Angle of less than 39 degrees" , "Severe, penetrating" , "Sharp like angle" .)