Weight revealed with no uncertainy? Not entirely (5)
I believe the answer is:
ounce
'weight' is the definition.
(unit of weight)
'with no uncertainy? not entirely' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'OUNCE' can be found hidden inside 'with no uncertainy'.
'revealed' is the link.
(Other definitions for ounce that I've seen before include "Unit of weight; cat" , "16 for a pound" , "Weight; big cat" , "Large cat" , "On cue (anag.)" .)