Crossword Genius

Set of three considered as a unit (5)

Ross

I believe the answer is:

triad

(Other definitions for triad that I've seen before include "Group or set of three" , "Chinese secret society" , "Criminals" , "three making a sound?" , "Three-note chord -- Chinese criminal gang" .)

I've seen this clue in The Telegraph.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.