Bizarre runes one observed in hospital? (5)

I believe the answer is:

nurse

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'one observed in hospital?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'bizarre runes' is the wordplay.
'bizarre' indicates anagramming the letters.
'runes' with letters rearranged gives 'NURSE'.

Can you help me to learn more?

(Other definitions for nurse that I've seen before include "Nourish" , "one working in theatre" , "Medical carer" , "drink slowly" , "Hospital tender" .)

I've seen this clue in The Times.

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