chimneypiece vs mantelpiece

chimneypiece and mantelpiece both are nouns.

Word	Noun	Adjective	Verb	Adverb
chimneypiece	Yes	No	No	No
mantelpiece	Yes	No	No	No

As nouns, chimneypiece and mantelpiece are synonyms defined as:

chimneypiece and mantelpiece: shelf that projects from wall above fireplace

Other synonyms of chimneypiece include mantel, mantle, mantlepiece.

chimneypiece (noun)	mantelpiece (noun)
shelf that projects from wall above fireplace	shelf that projects from wall above fireplace