French word ciel comes from Latin caedo, Proto-Indo-European *keh₂i-
caedo (Latin)
Cut, hew, fell.. Defeat decisively (defeat with heavy losses to the enemy side).. Kill.. Strike, beat.
*keh₂i- (Proto-Indo-European)
*kailom (Proto-Italic)
caelestem (Latin)
ciel (Old French)
Heaven.
ciel (French)
Canopy (of a bed, etc.) Heaven. Sky Heavens!.