"to keep safe, preserve from loss or decay," late 14c., from Old French conserver (9c.), from Latin 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"). Related: Conserved; conserving.
As a noun (often conserves) from late 14c. as "that which preserves;" early 15c. as "a confection, something preserved with sugar, etc."