Spookiest retirees heading off delirium (7)

I believe the answer is:

eeriest

I'm a little stuck... Click here to teach me more about this clue!

'spookiest' is the definition.
('eery' can be a synonym of 'spooky')

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for eeriest that I've seen before include "Most ghostly" , "Weirdest, I.e., trees are wierd" , "Most weird" , "Most strange and frightening" , "Strangest" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.