Frequently somewhat aloof, tentative (5)
I believe the answer is:
often
'frequently' is the definition.
('often' can be a synonym of 'frequently')
'somewhat aloof tentative' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'OFTEN' can be found hidden inside 'aloof tentative'.
(Other definitions for often that I've seen before include "occurring with frequency" , "Frequently, at short intervals" , "Frequently, many times" , "on many occasions" , "Perhaps daily" .)