Three got confused jointly (8)
I believe the answer is:
together
'jointly' is the definition.
(synonyms)
'three got confused' is the wordplay.
'confused' is an anagram indicator.
'three'+'got'='threegot'
'threegot' anagrammed gives 'TOGETHER'.
(Other definitions for together that I've seen before include "without a break?" , "In combination" , "tied" , "In company or in conjunction" , "Married" .)