Better uniform worn by old fool (6)
I believe the answer is:
outwit
'better' is the definition.
(I've seen this before)
'uniform worn by old fool' is the wordplay.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'worn by' means one lot of letters goes inside another (I've seen this in other clues).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'fool' becomes 'twit' (both can mean a stupid person).
'o'+'twit'='otwit'
'u' going within 'otwit' is 'OUTWIT'.
(Other definitions for outwit that I've seen before include "Dupe" , "Be too clever for, get the better of" , "Outsmart" , "Surpass in ingenuity" , "Be too smart for, defeat" .)