Conserve

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late Middle English: from Old French conserver (verb), conserve (noun), from Latin conservare ‘to preserve’, from con- ‘together’ + servare ‘to keep’.

wiktionary

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From Old French conserver, from Latin conservare(“to keep, preserve”), from com- (intensive prefix) + servo(“keep watch, maintain”). See also observe.

etymonline

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conserve (v.)

"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 perhaps 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."