Initially tense, hesitant and wary, become more relaxed (4)
I believe the answer is:
thaw
'become more relaxed' is the definition.
'initially tense hesitant and wary' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'tense hesitant and wary' is 'THAW'.
(Other definitions for thaw that I've seen before include "Unfreeze, defrost" , "when the temperature rises?" , "Melt; John --, actor" , "following 28 [SILVER]" , "detente" .)