Fashionable Post Office, one found by river naturally (5)
I believe the answer is:
hippo
'river naturally' is the definition.
I can't judge whether this definition defines the answer.
'fashionable post office one found by' is the wordplay.
'fashionable' becomes 'hip' (I've seen this in another clue).
'post office' becomes 'po' (abbreviation).
'one found by' means one lot of letters go next to another.
'hip'+'po'='HIPPO'
Can you help me to learn more?
(Other definitions for hippo that I've seen before include "Augustine's place" , "Wallowing creature" , "Large wallower (abbr)" , "22 aquatic animal" , "African wallower (abbr)" .)