Locates mislaid sugar (7)
I believe the answer is:
lactose
'sugar' is the definition.
(I know that lactose is a type of disaccharide)
'locates mislaid' is the wordplay.
'mislaid' is an anagram indicator.
'locates' anagrammed gives 'LACTOSE'.
(Other definitions for lactose that I've seen before include "Sugar found in milk" , "Part of milk" , "A sugar present in milk" , "White substance in milk" , "Constituent of milk" .)