Big cougar originally aboard ship, wild feline (6)
I believe the answer is:
bobcat
'wild feline' is the definition.
(I've seen this in another clue)
'big cougar originally aboard ship' is the wordplay.
'originally' says to take the initial letters.
'aboard' is an insertion indicator.
'ship' becomes 'boat' (I've seen this before).
The initial letters of 'big cougar' is 'bc'.
'bc' placed inside 'boat' is 'BOBCAT'.
(Other definitions for bobcat that I've seen before include "North American feline" , "American native" , "A sort of lynx" , "Small N American lynx" , "Bay lynx" .)