Tramp returning with incomplete clue? One's supposedly intelligent! (7)
I believe the answer is:
dolphin
'one's supposedly intelligent' is the definition.
(dolphins are intelligent animals)
'tramp returning with incomplete clue?' is the wordplay.
'tramp' becomes 'plod' (I've seen this before).
'returning' says the letters should be written in reverse.
'with' means one lot of letters go next to another.
'incomplete' means to remove the last letter.
'clue?' becomes 'hint' ('hint' can be a synonym of 'clue').
'plod' in reverse letter order is 'dolp'.
'hint' with its last letter taken off is 'hin'.
'dolp'+'hin'='DOLPHIN'
(Other definitions for dolphin that I've seen before include "swimmer" , "Sea mammal like large porpoise, friendly towards people" , "Relative of whale" , "Intelligent marine mammal" , "Small toothed whale, larger than a porpoise" .)