Sailor provided force for excise (6)
I believe the answer is:
tariff
'excise' is the definition.
(thesaurus)
'sailor provided force' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'provided' becomes 'if'.
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'tar'+'if'+'f'='TARIFF'
'for' acts as a link.
(Other definitions for tariff that I've seen before include "Tax or duty to be paid on some imports or exports" , "List of prices or charges" , "List of prices displayed as in pub" , "Import or export duty" , "Customs-duty" .)