Fish biting line in Arctic (4)
I believe the answer is:
cold
'arctic' is the definition.
(similar in meaning)
'fish biting line' is the wordplay.
'fish' becomes 'cod' (type of fish).
'biting' means one lot of letters goes inside another (some letters bite or swallow others).
'line' becomes 'l' (used when specifying particular lines from a poem).
'cod' enclosing 'l' is 'COLD'.
'in' acts as a link.
(Other definitions for cold that I've seen before include "Lacking warmth" , "Frigid" , "Unemotional; wintry" , "At low temperature" , "Unemotional; infection" .)