Perfect, perhaps, under pressure (5)
I believe the answer is:
tense
I believe this clue is a double definition.
'perfect perhaps' is the first definition.
(grammar)
'under pressure' is the second definition.
(I've seen this before)
(Other definitions for tense that I've seen before include "Anxious, high-strung" , "Suffering from strain" , "On edge" , "Verb form indicating time" , "Present, possibly" .)