Locket

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late Middle English (in locket (sense 2)): from Old French locquet, diminutive of loc ‘latch, lock’, of Germanic origin; related to lock1. locket (sense 1) dates from the late 17th century.

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From French loquet, from a diminutive of Anglo-Norman loc, itself from Old English loc.

etymonline

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locket (n.)

mid-14c., "iron cross-bar of a window," from Old French loquet "door-handle, bolt, latch, fastening" (14c.), diminutive of loc "lock, latch," from Frankish or some other Germanic source (compare Old Norse lok "fastening, lock;" see lock (n.1)). Meaning "little ornamental case with hinged cover" (containing a lock of hair, miniature portrait, etc.) first recorded 1670s. Italian lucchetto also is from Germanic.