casting vs life mask

casting and life mask both are nouns.

Word	Noun	Adjective	Verb	Adverb
casting	Yes	No	No	No
life mask	Yes	No	No	No

As nouns, life mask is a hyponym of casting; that is, life mask is a word with a more specific, narrower meaning than casting:

Other hyponyms of casting include death mask, block, cylinder block, engine block.

casting (noun)	life mask (noun)
the act of creating something by casting it in a mold	a cast taken from the face of a living person
the act of throwing a fishing line out over the water by means of a rod and reel
the choice of actors to play particular roles in a play or movie
object formed by a mold