Quietly divide up onion (7)
I believe the answer is:
shallot
'onion' is the definition.
(I know that shallot is a type of onion)
'quietly divide up' is the wordplay.
'quietly' becomes 'sh' (both are used to tell someone to be quiet).
'divide up' becomes 'allot' (I've seen this in another clue).
'sh'+'allot'='SHALLOT'
(Other definitions for shallot that I've seen before include "Host all with kind of onion" , "Species of onion" , "salad vegetable" , "Small onion" , "Edible onion-like bulb" .)