Sailor originally keeping an otter (5)
I believe the answer is:
tarka
'otter' is the definition.
(I've seen this before)
'sailor originally keeping an' is the wordplay.
'sailor' becomes 'tar' (tar can mean a sailor).
'originally' indicates taking the first letters.
The first letters of 'keeping an' is 'ka'.
'tar'+'ka'='TARKA'
(Other definitions for tarka that I've seen before include "One after fish booked" , "Fictional otter" , "Swimmer in story" , "Henry Williamson's otter" , "Devon swimmer" .)