A pensive time initially is suitable (3)
I believe the answer is:
apt
'suitable' is the definition.
(apt means appropriate or fitting)
'a pensive time initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'pensive time' is 'pt'.
'a'+'pt'='APT'
'is' is the link.
(Other definitions for apt that I've seen before include "Suitable; quick to learn" , "Befitting" , "suitable for the circumstances" , "Apposite, appropriate" , "flat" .)