To enlist oneself (in something) or become a member (of something)
To enter (a name, etc.) in a register, roll or list
To enlist (someone) or make (someone) a member of
To keep in possession or use.
To employ by paying a retainer.
To hold back (a pupil) instead of allowing them to advance to the next class or year.
To keep in one's pay or service.
To hold secure.