Weight not right on cue (5)
I believe the answer is:
ounce
'weight' is the definition.
(unit of weight)
'not right on cue' is the wordplay.
'not right' indicates anagramming the letters.
'on'+'cue'='oncue'
'oncue' is an anagram of 'OUNCE'.
(Other definitions for ounce that I've seen before include "One-sixteenth of pound" , "weight? Surely not" , "Imperial unit of weight" , "one of a number in the pound" , "16 for a pound" .)