Christopher Columbus's port of call (4)

I believe the answer is:

stop

I'm a little stuck... Click here to teach me more about this clue!

'port of call' is the definition.
(I've seen this before)

'christopher columbus's' is the wordplay.
'STOP' is hidden within the letters.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for stop that I've seen before include "Bung" , "Check" , "period in US" , "Cease, halt" , "Come to a halt" .)

I've seen this clue in the Evening Standard.

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