Fat officer with old sailor aboard vessel (5,6)
I believe the answer is:
cocoa butter
'fat' is the definition.
(I know that cocoa-butter is a type of fat)
'officer with old sailor aboard vessel' is the wordplay.
I cannot really understand how this works, but
'officer' could be 'oc' (I've seen this in other clues) and 'oc' is found in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found within the answer.
'sailor' could be 'ab' (abbreviation for able seaman) and 'ab' is found within the answer.
'vessel' could be 'cutter' (cutter is a kind of vessel) and 'cutter' is found in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for cocoa butter that I've seen is " True tobacco (anag) -- basis of chocolate".)