Retired teacher greeting Hindu sage (5)
I believe the answer is:
rishi
'hindu sage' is the definition.
(I've seen this before)
'retired teacher greeting' is the wordplay.
'retired' says the letters should be written backwards.
'teacher' becomes 'sir' (way of addressing a male teacher).
'greeting' becomes 'hi' (hi is a kind of greeting).
'sir' written backwards gives 'ris'.
'ris'+'hi'='RISHI'
(Other definitions for rishi that I've seen before include "Poet" , "wise man" , "Spiritual leader" , "Guru" , "Revered man" .)