Legendary figure, very large one, in hospital (6)

I believe the answer is:

ossian

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'legendary figure' is the definition.
The definition suggests a singular noun which matches the answer.

'very large one in hospital' is the wordplay.
'very large' becomes 'os' (abbreviation for oversize).
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'hospital' becomes 'san' (I've seen this in other clues).
'i' going inside 'san' is 'sian'.
'os'+'sian'='OSSIAN'

Can you help me to learn more?

(Other definitions for ossian that I've seen before include "Gaelic bard, son of Fingal" , "Legendary Cthree Gaelic bard" , "Fictitious Irish poet" , "Legendary Gaelic poet faked by Macpherson" , "Invented Irish hero" .)

I've seen this clue in The Times.

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