Allowance taken from Horatio Nelson (6)
I believe the answer is:
ration
'allowance' is the definition.
(thesaurus)
'taken from horatio nelson' is the wordplay.
'taken from' indicates the answer is hidden within the clue.
'RATION' is hidden in the letters of 'horatio nelson'.
(Other definitions for ration that I've seen before include "Limit quantity as of food during scarcity" , "Limit to a fixed amount, be sparing" , "One's allotted portion" , "Dole out in measured quantities, as in time of shortage" , "A fixed quantity allowed to one person in times of scarcity" .)