When weak Ray moves to hospital (9)

I believe the answer is:

infirmary

I'm a little stuck... Click here to teach me more about this clue!

'to hospital' is the definition.
(synonyms)

'when weak ray moves' is the wordplay.
'when weak' becomes 'infirm' (synonyms. I am not sure about the 'when' bit.).
'moves' is an anagram indicator.
'ray' is an anagram of 'ary'.
'infirm'+'ary'='INFIRMARY'

Can you help me to learn more?

(Another definition for infirmary that I've seen is " Hospital".)

I've seen this clue in The Globe and Mail.

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