Ring the embassy - something's been left out (8)

I believe the answer is:

omission

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'something's been left out' is the definition.
I can't judge whether this definition defines the answer.

'ring the embassy' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'the embassy' becomes 'mission' (I've seen this before).
'o'+'mission'='OMISSION'

Can you help me to learn more?

(Other definitions for omission that I've seen before include "cut?" , "It may create space" , "Lack" , "Mistake resulting from neglect" , "Something lacking" .)

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

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