Turn, on cue, to make weight (5)
I believe the answer is:
ounce
'weight' is the definition.
(I know that ounce is a type of apothecaries\\u0027 unit)
'turn on cue' is the wordplay.
'turn' indicates anagramming the letters.
'on'+'cue'='oncue'
'oncue' with letters rearranged gives 'OUNCE'.
'to make' acts as a link.
(Other definitions for ounce that I've seen before include "A light imperial measure of weight" , "prowler" , "Atom" , "scrap" , "weight? Surely not" .)