Cask is for port in North Africa (5)
I believe the answer is:
tunis
'port in north africa' is the definition.
'tunis' can be an answer for 'port' (I've seen this before). I also know that 'africa' relates to this answer.
'cask is' is the wordplay.
'cask' becomes 'tun' (tun is a kind of cask).
'tun'+'is'='TUNIS'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for tunis that I've seen before include "North African location" , "North African port and capital" , "Tom, Dick or Harry" , "Carthage lies near this N. African city" , "I stun (anag) - port and capital" .)