A great cry of 'Stop' (5)

I believe the answer is:

avast

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'cry of stop' is the definition.
'avast' can be an answer for 'stop' (I've seen this before). I'm not sure about the 'cry of' bit.

'a great' is the wordplay.
'great' becomes 'vast' (I've seen this before).
'a'+'vast'='AVAST'

Can you help me to learn more?

(Other definitions for avast that I've seen before include "eleven [CEASE] at sea" , "Stop! (naut.)" , "Stop sailing" , "Hold fast! (naut.)" , "order for tar" .)

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

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