Fart once and be worried for 'friend (10)
I believe the answer is:
benefactor
''friend' is the definition.
(thesaurus)
'fart once and be worried' is the wordplay.
'and' means one lot of letters go next to another.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
'fart'+'once'='fartonce'
'fartonce' after 'be' is 'befartonce'.
'befartonce' is an anagram of 'BENEFACTOR'.
'for' is the link.
(Other definitions for benefactor that I've seen before include "Patron, sponsor" , "One giving money to a cause" , "Patronising sort" , "charity supporter?" , "One provides bread" .)