stigma vs demerit

stigma and demerit both are nouns.

Word	Noun	Adjective	Verb	Adverb
stigma	Yes	No	No	No
demerit	Yes	No	No	No

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

stigma: a symbol of disgrace or infamy
demerit: a mark against a person for misconduct or failure; usually given in school or armed forces

Other hyponyms of stigma include bar sinister, bend sinister, cloven foot, cloven hoof.

stigma (noun)	demerit (noun)
a skin lesion that is a diagnostic sign of some disease	the quality of being inadequate or falling short of perfection
an external tracheal aperture in a terrestrial arthropod	a mark against a person for misconduct or failure; usually given in school or armed forces
a symbol of disgrace or infamy
the apical end of the style where deposited pollen enters the pistil