Joins up (7)
'joins up' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for enlists that I've seen before include "Listens (anag.)" , "gets involved" , "Recruits" , "Joins up" , "volunteers" .)
(Other definitions for enrols that I've seen before include "Registers name" , "Enlists" , "Joins up, signs on" , "Enters on a list" , "Registers as a member" .)