A major, maybe, on southern islands (4)
I believe the answer is:
keys
'islands' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps you can see an association between them that I don't see?
'a major maybe on southern' is the wordplay.
'a major maybe' becomes 'key' (I've seen this in another clue).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'southern' becomes 's' (abbreviation).
'key'+'s'='KEYS'
Can you help me to learn more?
(Other definitions for keys that I've seen before include "Lower House of the Isle of Man parliament" , "Bunch of openers?" , "Landing places" , "Musical scales" , "Solutions" .)