Twelve months in port (3)
I believe the answer is:
ayr
'port' is the definition.
(I know that Ayr is an port)
'twelve months' is the wordplay.
I cannot quite understand how this works, but
'twelve months' could be 'yr' (yr is abbreviation for year) and 'yr' is found in the answer.
A single letter 'a' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for ayr that I've seen before include "Scottish town, port and racecourse" , "Scots. town; sounds like song" , "Town in Strathclyde" , "Scots port on Firth of Clyde" , "Scottish resort" .)