mannikin vs small person

mannikin and small person both are nouns.

Word	Noun	Adjective	Verb	Adverb
mannikin	Yes	No	No	No
small person	Yes	No	No	No

As nouns, small person is a hypernym of mannikin; that is, small person is a word with a broader meaning than mannikin:

mannikin: a person who is very small but who is not otherwise deformed or abnormal
small person: a person of below average size

mannikin (noun)	small person (noun)
a life-size dummy used to display clothes	a person of below average size
a person who is very small but who is not otherwise deformed or abnormal
a woman who wears clothes to display fashions