playground vs grounds

playground and grounds both are nouns.

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

As nouns, grounds is a hypernym of playground; that is, grounds is a word with a broader meaning than playground:

Other hypernyms of playground include curtilage, yard.

playground (noun)	grounds (noun)
yard consisting of an outdoor area for children's play	the enclosed land around a house or other building
an area where many people go for recreation, holidays or other purposes	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