Jack's contribution to a rate rise (3)

I believe the answer is:

tar

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'jack's' is the definition.
(both are informal terms for sailor)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tar that I've seen before include "Liquid from wood, coal" , "Kind of rat for sailor" , "Jack ..., British sailor" , "It may cover the road" , "Seaman; pitch" .)

I've seen this clue in the Evening Standard.

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