United, embracing fool (3)
I believe the answer is:
nit
'fool' is the definition.
(both can mean a stupid person)
'united embracing' is the wordplay.
'embracing' says the answer is hidden in the clue (the solution is embraced by words in the clue).
'NIT' is hidden in the letters of 'united'.
(Other definitions for nit that I've seen before include "no egghead?" , "Hair louse" , "Parasite's egg made of tin" , "Cause of much head-scratching" , "Idiot, ass" .)