A small bird behind a boat (6)
I believe the answer is:
astern
'a small bird behind a boat' is the definition.
I can't tell whether this defines the answer.
'a small bird behind a' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'bird' becomes 'tern' (tern is a kind of bird).
'behind' is a charade indicator (letters next to each other).
's'+'tern'='stern'
'stern' put after 'a' is 'ASTERN'.
Can you help me to learn more?
(Other definitions for astern that I've seen before include "Aft" , "Nautically behind" , "Behind (naut.)" , "Behind at sea" , "Abaft" .)