To make invalid. Especially applied to contract law.
To make or declare (an argument, statement, or theory) unsound or erroneous; disprove.
To render invalid; discredit.
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 keep in possession or use.
To hold secure.