capsule vs eyeball

capsule and eyeball both are nouns.

Word	Noun	Adjective	Verb	Adverb
capsule	Yes	No	Yes	No
eyeball	Yes	No	Yes	No

As nouns, eyeball is a hyponym of capsule; that is, eyeball is a word with a more specific, narrower meaning than capsule:

Other hyponyms of capsule include malpighian body, malpighian corpuscle, renal corpuscle, orb, lens capsule.

capsule (noun)	eyeball (noun)
a pill in the form of a small rounded gelatinous container with medicine inside	the ball-shaped capsule containing the vertebrate eye
a spacecraft designed to transport people and support human life in outer space
a small container
a pilot's seat in an airplane that can be forcibly ejected in the case of an emergency; then the pilot descends by parachute
a structure that encloses a body part
a shortened version of a written work
a dry dehiscent seed vessel or the spore-containing structure of e.g. mosses

capsule (verb)	eyeball (verb)
put in a short or concise form; reduce in volume	look at
enclose in a capsule