One basks in sun in docked vessel (4)
I believe the answer is:
croc
'one basks in sun' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'docked vessel' is the wordplay.
'docked' means to remove the last letter (to dock can mean to remove the tail of an animal).
'vessel' becomes 'crock' (crock is a type of vessel or container).
'crock' with its final letter taken away is 'CROC'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for croc that I've seen before include "Large predatory reptile (colloq.)" , "Fierce beast" , "Reptile (abbrev.)" , "African beast; sounds like piece of pot" , "Fierce reptile" .)