1humorous with object Make (someone) unable to think clearly; confuse.
- ‘being in love must have addled your brain’
2no object (of an egg) become rotten, producing no chick.
- ‘the extremely hot and dry weather had caused the eggs to addle’
(of an egg) rotten.
Middle English (in addle (adjective)): from Old English adela ‘liquid filth’, of Germanic origin; related to Dutch aal and German Adel ‘mire, puddle’.