gridiron vs playing field

gridiron and playing field both are nouns.

Word	Noun	Adjective	Verb	Adverb
gridiron	Yes	No	No	No
playing field	Yes	No	No	No

As nouns, playing field is a hypernym of gridiron; that is, playing field is a word with a broader meaning than gridiron:

Other hypernyms of gridiron include athletic field, field, playing area.

gridiron (noun)	playing field (noun)
a cooking utensil of parallel metal bars; used to grill fish or meat	a piece of land prepared for playing a game
the playing field on which football is played	the circumstances under which competition occurs