tall-grass vs tallgrass

tall-grass and tallgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
tall-grass	Yes	No	No	No
tallgrass	Yes	No	No	No

As nouns, tall-grass and tallgrass are synonyms defined as:

tall-grass and tallgrass: any of various grasses that are tall and that flourish with abundant moisture

tall-grass (noun)	tallgrass (noun)
any of various grasses that are tall and that flourish with abundant moisture	any of various grasses that are tall and that flourish with abundant moisture