Learned person and I had returned in flat-bottomed boat (6)
I believe the answer is:
pundit
'learned person' is the definition.
(synonyms)
'i had returned in flat-bottomed boat' is the wordplay.
'i had' becomes 'i'd' (I'd).
'returned' says the letters should be written in reverse.
'in' indicates putting letters inside.
'flat-bottomed boat' becomes 'punt' (I've seen this in another clue).
'id' backwards is 'di'.
'di' put within 'punt' is 'PUNDIT'.
'and' is the link.
(Other definitions for pundit that I've seen before include "Learned Hindu or general expert" , "Subject expert" , "Expert in a particular field, often consulted" , "An expert or critic in a particular field" , "Expert (sometimes self-appointed)" .)