Enlist loner, somehow (5)
I believe the answer is:
enrol
'enlist' is the definition.
(I know that enlist is a more specific form of the action enrol)
'loner somehow' is the wordplay.
'somehow' indicates anagramming the letters.
'loner' with letters rearranged gives 'ENROL'.
(Other definitions for enrol that I've seen before include "Join up, sign on" , "Add to list of members" , "register for classes" , "Enlist" , "Loner inclined to join in" .)