grounds vs backyard

grounds and backyard both are nouns.

Word	Noun	Adjective	Verb	Adverb
grounds	Yes	No	No	No
backyard	Yes	No	No	No

As nouns, backyard is a hyponym of grounds; that is, backyard is a word with a more specific, narrower meaning than grounds:

Other hyponyms of grounds include dooryard, front yard, garden, playground, side yard.

grounds (noun)	backyard (noun)
the enclosed land around a house or other building	the grounds in back of a house
your basis for belief or disbelief; knowledge on which to base belief
a justification for something existing or happening
a tract of land cleared for some special purposes (recreation or burial etc.)
dregs consisting of solid particles (especially of coffee) that form a residue