athar vs attar of roses

athar and attar of roses both are nouns.

Word	Noun	Adjective	Verb	Adverb
athar	Yes	No	No	No
attar of roses	Yes	No	No	No

As nouns, attar of roses is a hyponym of athar; that is, attar of roses is a word with a more specific, narrower meaning than athar:

athar: essential oil or perfume obtained from flowers
attar of roses: a volatile fragrant oil obtained from fresh roses by steam distillation

Other hyponyms of athar include rose oil.

athar (noun)	attar of roses (noun)
essential oil or perfume obtained from flowers	a volatile fragrant oil obtained from fresh roses by steam distillation