D defs.my
Entry 2 senses Webster, 1913

Trio

/trē'-ōˌ/ · Tri·o · IPA /ˈtɹioʊ/
01 n. Three, considered collectively; three in company or acting together; a set of three; three united.
  1. 1.
    Three, considered collectively; three in company or acting together; a set of three; three united.
    “The trio were well accustomed to act together, and were linked to each other by ties of mutual interest.” Dickens.
  2. 2.
    A composition for three parts or three instruments.(Mus.)