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 pay money, to disburse; especially, to pay a great deal of money.
To use a program's "shell escape" function to execute an unrelated command or to invoke a subsidiary, interactive shell.