Teacher turned up, greeting Hindu sage (5)
I believe the answer is:
rishi
'hindu sage' is the definition.
(term for a Hindu sage or wiseman)
'teacher turned up greeting' is the wordplay.
'teacher' becomes 'sir' (way of addressing a male teacher).
'turned up' shows that the letters should be reversed in order.
'greeting' becomes 'hi' (hi is a kind of greeting).
'sir' back-to-front is 'ris'.
'ris'+'hi'='RISHI'
(Other definitions for rishi that I've seen before include "Spiritual leader" , "Hindu sage or saint" , "wise man" , "Poet" , "Guru" .)