trichroism vs pleochroism

trichroism and pleochroism both are nouns.

Word	Noun	Adjective	Verb	Adverb
trichroism	Yes	No	No	No
pleochroism	Yes	No	No	No

As nouns, pleochroism is a hypernym of trichroism; that is, pleochroism is a word with a broader meaning than trichroism:

trichroism: pleochroism of a crystal so that it exhibits three different colors when viewed from three different directions
pleochroism: the phenomenon of different colors appearing when certain crystals are viewed from different directions

trichroism (noun)	pleochroism (noun)
pleochroism of a crystal so that it exhibits three different colors when viewed from three different directions	the phenomenon of different colors appearing when certain crystals are viewed from different directions