sib vs twin

sib and twin both are nouns.

Word	Noun	Adjective	Verb	Adverb
sib	Yes	No	No	No
twin	Yes	Yes	Yes	No

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

Other hyponyms of sib include half blood, quad, quadruplet, quin, quint, quintuplet, triplet.

sib (noun)	twin (noun)
one related by blood or origin; especially on sharing an ancestor with another	a duplicate copy
a person's brother or sister	either of two offspring born at the same time from the same pregnancy

sib (adjective)	twin (adjective)
	being two identical

sib (verb)	twin (verb)
	give birth to twins
	grow as twins
	bring two objects, ideas, or people together
	duplicate or match