eyecup vs eye cup

eyecup and eye cup both are nouns.

Word	Noun	Adjective	Verb	Adverb
eyecup	Yes	No	No	No
eye cup	Yes	No	No	No

As nouns, eyecup and eye cup are synonyms defined as:

eyecup and eye cup: a small vessel with a rim curved to fit the orbit of the eye; use to apply medicated or cleansing solution to the eyeball

Other synonyms of eyecup include eyebath.

eyecup (noun)	eye cup (noun)
(embryology) a two-walled cuplike depression that develops into the pigmented and sensory layers of the retina	a small vessel with a rim curved to fit the orbit of the eye; use to apply medicated or cleansing solution to the eyeball
a small vessel with a rim curved to fit the orbit of the eye; use to apply medicated or cleansing solution to the eyeball