Once a year idealists leave Aleutian Islands (6)
I believe the answer is:
annual
'once a year' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for annual that I've seen before include "yearly event" , "Book; occurring once a year" , "Plant that lives and dies within one year" , "Occuring once a year" , "Hardy it may be" .)