I had each brainwave (4)

I believe the answer is:

idea

'brainwave' is the definition.
(I've seen this in another clue)

'i had each' is the wordplay.
'i had' becomes 'i'd' (I'd).
'each' becomes 'ea' (abbreviation).
'id'+'ea'='IDEA'

(Other definitions for idea that I've seen before include "Creative spark" , "Plan" , "Content of cognition" , "Intention" , "Mental impression" .)

I've seen this clue in The Times.

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.