playing area vs diamond

playing area and diamond both are nouns.

Word	Noun	Adjective	Verb	Adverb
playing area	Yes	No	No	No
diamond	Yes	No	No	No

As nouns, diamond is a hyponym of playing area; that is, diamond is a word with a more specific, narrower meaning than playing area:

playing area (noun)	diamond (noun)
a piece of land prepared for playing a game	the area of a baseball field that is enclosed by 3 bases and home plate
	a playing card in the minor suit that has one or more red rhombuses on it
	the baseball playing field
	a transparent piece of diamond that has been cut and polished and is valued as a precious gem
	a parallelogram with four equal sides; an oblique-angled equilateral parallelogram
	very hard native crystalline carbon valued as a gem