trio vs tierce

trio and tierce both are nouns.

Word	Noun	Adjective	Verb	Adverb
trio	Yes	No	No	No
tierce	Yes	No	No	No

As nouns, trio and tierce are synonyms defined as:

trio and tierce: the cardinal number that is the sum of one and one and one

trio (noun)	tierce (noun)
a musical composition for three performers	one of three equal parts of a divisible whole
three people considered as a unit	the cardinal number that is the sum of one and one and one
a set of three similar things considered as a unit	the third canonical hour; about 9 a.m.
three performers or singers who perform together
the cardinal number that is the sum of one and one and one