altarpiece vs reredos

altarpiece and reredos both are nouns.

Word	Noun	Adjective	Verb	Adverb
altarpiece	Yes	No	No	No
reredos	Yes	No	No	No

As nouns, altarpiece and reredos are synonyms defined as:

altarpiece and reredos: a painted or carved screen placed above and behind an altar or communion table

altarpiece (noun)	reredos (noun)
a painted or carved screen placed above and behind an altar or communion table	a painted or carved screen placed above and behind an altar or communion table