Gruff sailor on Channel seizing power (6)
I believe the answer is:
abrupt
'gruff' is the definition.
(thesaurus)
'sailor on channel seizing power' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'on' says to put letters next to each other.
'channel' becomes 'rut' (I've seen this before).
'seizing' means one lot of letters goes inside another.
'power' becomes 'p'.
'rut' going around 'p' is 'rupt'.
'ab'+'rupt'='ABRUPT'
(Other definitions for abrupt that I've seen before include "Sudden; hasty, curt" , "Terse and sudden" , "Impolite" , "Short in manner" , "Sudden - blunt" .)