Extremely sorry about winter in Calais being cold (7)
I believe the answer is:
shivery
'being cold' is the definition.
(similar in meaning)
'extremely sorry about winter in' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'about winter' becomes 'hiver' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'sorry' with its middle taken out is 'sy'.
'sy' enclosing 'hiver' is 'SHIVERY'.
'calais' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for shivery that I've seen is " Affected by cold".)