°A
requirement which must be satisfied before taking a course of action.
"A marriage licence is a precondition for a wedding."
verb
"{{quote-journal|1996|C. Weinbrenner et al.|Loss of glycogen during preconditioning is not a prerequisite for protection of the rabbit heart |Basic Research in Cardiology|volume=91|issue=5|url=http://www.springerlink.com/content/k83x3755723r13l3/"