Most pure Charles facing ordeal? (8)

I believe the answer is:

chastest

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'most pure' is the definition.
Both the answer and definition are superlative adjectives. Maybe they are linked in a way I don't understand?

'charles facing ordeal?' is the wordplay.
'charles' becomes 'Chas' (shortened form).
'facing' says to put letters next to each other.
'ordeal?' becomes 'test' (a testing situation).
'chas'+'test'='CHASTEST'

Can you help me to learn more?

(Another definition for chastest that I've seen is " Most pure and virginal".)

I've seen this clue in The Times.

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