cygnet:  A cygnet is literally a ‘small swan’. The late Old French term for ‘swan’ was cigne, and this was modified with the diminutive suffix -et, probably in Anglo-Norman, to produce *cignet, the source of the English word. Cigne, precursor of modern French cygne, strikes a familiar chord, but in fact its Latin source, cygnus, is a comparatively late development. The standard classical Latin word for ‘swan’ was cycnus, from Greek kúknos, which produced in early Old French cisne. A trace of it survives in Spanish cisne ‘swan’.
c. 1400, also signet before 17c., from Anglo-French, diminutive of Old French cigne, cisne "swan" (12c., Modern French cygne), from Latin cygnus, from Greek kyknos, perhaps from PIE *keuk- "to be white."