lamb vs lambkin

lamb and lambkin both are nouns.

Word	Noun	Adjective	Verb	Adverb
lamb	Yes	No	Yes	No
lambkin	Yes	No	No	No

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

Other hyponyms of lamb include baa-lamb, hog, hogg, hogget, teg, Persian lamb.

lamb (noun)	lambkin (noun)
young sheep	a very young lamb
the flesh of a young domestic sheep eaten as food
a sweet innocent mild-mannered person (especially a child)
a person easily deceived or cheated (especially in financial matters)

lamb (verb)	lambkin (verb)
give birth to a lamb