Not relaxed in past, perhaps (5)
I believe the answer is:
tense
This clue is a double definition.
'not relaxed' is the first definition.
('tense' is the opposite to 'relaxed')
'past perhaps' is the second definition.
(grammar)
'in' is the link.
(Other definitions for tense that I've seen before include "in the past, perhaps" , "Taut - timely verbal indication" , "under pressure" , "Stretched tightly, unable to relax" , "present, perhaps?" .)