pet food vs pet-food

pet food and pet-food both are nouns.

Word	Noun	Adjective	Verb	Adverb
pet food	Yes	No	No	No
pet-food	Yes	No	No	No

As nouns, pet food and pet-food are synonyms defined as:

Other synonyms of pet food include petfood.

pet food (noun)	pet-food (noun)
food prepared for animal pets	food prepared for animal pets