Pay off vessel going to old navy (6)
I believe the answer is:
suborn
'pay off' is the definition.
(thesaurus)
'vessel going to old navy' is the wordplay.
'vessel' becomes 'sub' (sub is a kind of vessel**).
'going to' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'navy' becomes 'rn' (abbreviation for Royal Navy).
'sub'+'o'+'rn'='SUBORN'
(Other definitions for suborn that I've seen before include "Bribe (someone) to break law" , "Induce to commit unlawful act through bribary" , "Legally, induce to commit perjury" , "Induce by bribery to do something wrong" , "Bribe for evil ends" .)