baby's breath vs babies'-breath

baby's breath and babies'-breath both are nouns.

Word	Noun	Adjective	Verb	Adverb
baby's breath	Yes	No	No	No
babies'-breath	Yes	No	No	No

As nouns, baby's breath and babies'-breath are synonyms defined as:

baby's breath and babies'-breath: tall plant with small lance-shaped leaves and numerous tiny white or pink flowers

Other synonyms of baby's breath include Gypsophila paniculata.

baby's breath (noun)	babies'-breath (noun)
tall plant with small lance-shaped leaves and numerous tiny white or pink flowers	tall plant with small lance-shaped leaves and numerous tiny white or pink flowers