half-moon vs lunula

half-moon and lunula both are nouns.

Word	Noun	Adjective	Verb	Adverb
half-moon	Yes	No	No	No
lunula	Yes	No	No	No

As nouns, half-moon and lunula are synonyms defined as:

half-moon and lunula: the crescent-shaped area at the base of the human fingernail

Other synonyms of half-moon include lunule.

half-moon (noun)	lunula (noun)
the crescent-shaped area at the base of the human fingernail	a crescent-shaped metal ornament of the Bronze Age
the time at which the Moon is at first or last quarter when half its face is illuminated	the crescent-shaped area at the base of the human fingernail