"un ciel", "des cieux" (masc.)
It's an irregular noun.
'Ciel' is the french word for 'Sky'.
l'arc-en-ciel, plural: des arcs-en-ciel.
Ciel
Sky in french.
Arc en ciel
Ciel (masc.)
In French, "Ciel" means either "sky" or "Heaven", depending on the context.
The French word for lady is dame, the plural of which is dames.
Le ciel in French means "the sky" in English.
"bleu ciel" means "sky blue" in French.
'ciel' (the sky) sounds likes the two letters 'C-L' in French.
It is plural and French.