water-mint vs water mint

water-mint and water mint both are nouns.

Word	Noun	Adjective	Verb	Adverb
water-mint	Yes	No	No	No
water mint	Yes	No	No	No

As nouns, water-mint and water mint are synonyms defined as:

water-mint and water mint: a European mint that thrives in wet places; has a perfume like that of the bergamot orange; naturalized in eastern North America

Other synonyms of water-mint include Mentha aquatica.

water-mint (noun)	water mint (noun)
a European mint that thrives in wet places; has a perfume like that of the bergamot orange; naturalized in eastern North America	a European mint that thrives in wet places; has a perfume like that of the bergamot orange; naturalized in eastern North America