To keep in one's pay or service.
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 possession or use.
To hold secure.
To agree to purchase some good or service.
To add one's own name to the list of people who are participating in something (including amateur, but not professional, teams)
To add a name to the list of people who are participating in something.