Surprise in a host's demeanour (8)

I believe the answer is:

astonish

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'surprise' is the definition.
(astonishing is a kind of surprising)

'in a host's demeanour' is the wordplay.
'in a host's' can be anagrammed to 'ASTONISH'.
But, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for astonish that I've seen before include "are staggering" , "Gobsmack" , "'knock for six'?" , "Greatly impress" , "Floor" .)

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

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