Teacher shown up, good day for wise guy (5)

I believe the answer is:

rishi

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'wise guy' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

'teacher shown up good day' is the wordplay.
'teacher' becomes 'sir' (way of addressing a male teacher).
'shown up' says the letters should be written in reverse (in a down clue, letters go up).
'good day' becomes 'hi'.
'sir' written backwards gives 'ris'.
'ris'+'hi'='RISHI'

'for' is the link.

Can you help me to learn more?

(Other definitions for rishi that I've seen before include "holy man" , "Hindu sage or saint" , "Guru" , "Spiritual leader" , "Revered man" .)

I've seen this clue in The Times.

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