Former islander's wacky mostly unknown pub located between islands (9)

'former islander's wacky mostly' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'unknown pub located between islands' is the wordplay.
I cannot quite see how this works, but
'unknown' could be 'z' (algebra) and 'z' is found within the answer.
'pub' could be 'bar' (both are drinking establishments) and 'bar' is found within the answer.
'islands' could be 'ii' (an abbreviation for island written twice) and 'ii' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?