Being hardened a summons is nothing to us (7)

I believe the answer is:

callous

'being hardened' is the definition.
(synonyms)

'a summons is nothing to us' is the wordplay.
'a summons' becomes 'call' (I've seen this in another clue).
'is nothing' becomes 'o' (O resembles 0).
'call'+'o'+'us'='CALLOUS'

(Other definitions for callous that I've seen before include "Cruel or unsympathetic" , "Cruelly unfeeling" , "Hard and unfeeling" , "Heartless" , "Not feeling" .)

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

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