A little bachelor needlessly going back for register (5)
I believe the answer is:
enrol
'for register' is the definition.
(enrolling is a kind of registering)
'a little bachelor needlessly going back' is the wordplay.
'a little' indicates a hidden word (a little bit of the clue).
'going back' is a reversal indicator.
'lorne' can be found hidden inside 'bachelor needlessly'.
'lorne' in reverse letter order is 'ENROL'.
(Other definitions for enrol that I've seen before include "register for classes" , "Record" , "Join up, sign on" , "Bring into service" , "Register officially" .)