c. 1400, "an official entrusted with the power and the duty to protect the interests or rights of someone else or some thing," from Anglo-French conservatour, from Latin conservator "keeper, preserver, defender," agent noun of conservare "to keep, preserve, keep intact, guard," from assimilated form of com-, here probably an intensive prefix (see com-), + servare "keep watch, maintain" (from PIE root *ser- (1) "to protect").
General sense of "a preserver" (from injury, violation, etc.) is from mid-15c. Fem. form conservatrice was used mid-15c. in reference to the Virgin.