Devious English quartet boarding vessel (7)
I believe the answer is:
evasive
'devious' is the definition.
(I've seen this before)
'english quartet boarding vessel' is the wordplay.
'english' becomes 'e' (abbreviation).
'quartet' becomes 'IV' (Roman numerals for four).
'boarding' means one lot of letters goes inside another.
'vessel' becomes 'vase' (vase is a kind of vessel).
'iv' going within 'vase' is 'vasive'.
'e'+'vasive'='EVASIVE'
(Other definitions for evasive that I've seen before include "Shifty, not answering directly" , "Avoiding giving answers" , "Shifty, equivocal" , "Deliberately vague" , "Not frank or responsive" .)