Permit European quietly aboard cutter (7)
I believe the answer is:
empower
'permit' is the definition.
(I've seen this before)
'european quietly aboard cutter' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'quietly' becomes 'p' (p for piano and quiet).
'aboard' means one lot of letters goes inside another.
'cutter' becomes 'mower' (I've seen this before).
'p' put into 'mower' is 'mpower'.
'e'+'mpower'='EMPOWER'
(Other definitions for empower that I've seen before include "Delegate" , "Give strength and confidence to" , "Entitle" , "Endow with authority" , "Sanction" .)