Sailor, northern, quiet about one stain (7)

I believe the answer is:

tarnish

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'one stain' is the definition.
(tarnish is a kind of stain)

'sailor northern quiet' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'quiet' becomes 'ish' (I can't explain this - if you can you should give a lot more credence to this answer).
'tar'+'n'+'ish'='TARNISH'

'about' is the link.

Can you help me to learn more?

(Other definitions for tarnish that I've seen before include "(Of metal) lose lustre" , "Cause to lose lustre, say silver" , "Film" , "Stain or blemish as with silverware" , "Take the shine off" .)

I've seen this clue in The Daily Express.

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