A huge shipping order? (5)

I believe the answer is:

avast

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'shipping order?' is the definition.
The definition and answer are not the same part of speech.

'a huge' is the wordplay.
'huge' 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 "Stop (nautical)" , ""stop" signal" , "Stop on board" , "shout stopping the ship" , "Stop, nautically speaking" .)

I've seen this clue in The Guardian, The Irish Independent, The Irish News, The Globe and Mail and The Telegraph.

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