Duo + one (5)
(Other definitions for three that I've seen before include "Figure" , "Number that's a crowd" , "Bears or blind mice" , "Subject of 1 9" , "Feet in 3 Down" .)
(Other definitions for trio that I've seen before include "Three together" , "Ensemble musical piece, eg Beethoven's 'Archduke'" , "Three of a kind" , "Riot (anag)" , "Chamber group" .)