Definition & Meaning of "addle brain"in English

What is the origin of the term "addle brain" and how is it used?

"Addle brain" is an English expression dating back to at least the 16th–17th centuries, combining "addle" (meaning spoiled, rotten, or confused, originally used for eggs) with "brain" to describe someone whose thinking is muddled or impaired. The term evokes the image of a brain that has gone "bad" or is incapable of clear thought. It has been used in informal speech, literature, and gentle insults to call someone foolish or confused. The phrase is mildly derogatory, usually playful rather than harsh, and rarely considered seriously offensive.