Philosopher left a shirt in river (5)
I believe the answer is:
plato
'philosopher' is the definition.
(Plato is an example)
'left a shirt in river' is the wordplay.
'left' becomes 'l' (common abbreviation**).
'shirt' becomes 't' (as in a T-shirt).
'in' is an insertion indicator.
'river' becomes 'po' (Italian river).
'l'+'a'+'t'='lat'
'lat' going into 'po' is 'PLATO'.
(Other definitions for plato that I've seen before include "Greek philosopher (The Republic)" , "Teacher of Aristotle, pupil of Socrates" , "Moon crater named after Greek philosopher" , "Republican writer?" , "Ancient Greek philosopher" .)