Monster disembowelled both weedy, vile sailors (6)
I believe the answer is:
wyvern
'monster' is the definition.
(I've seen this before)
'disembowelled both weedy vile sailors' is the wordplay.
'disembowelled both' says to hollow out the word (remove centre letters) (both words have their middle letters removed).
'vile sailors' becomes 'vern' (I can't justify this - if you can you should believe this answer much more).
'weedy' with its middle taken out is 'wy'.
'wy'+'vern'='WYVERN'
Can you help me to learn more?
(Other definitions for wyvern that I've seen before include "1950s Vauxhall model" , "Heraldic winged monster" , "Heraldic dragon with two legs and two wings" , "Heraldic beast" , "In heraldry, a dragon with wings, two legs and a barbed tail" .)