How did addled come to mean a person lacking in wit?

Answer:

The dictionary (Webster's 17th) shows that it went from Middle English meaning filth/liquid manure to "throw into confusion/confound" about 1712. I've heard the word addlepated (mixed up in the head), and I suppose that addled is the shortened version of that.

First answer by Simplemary. Last edit by Simplemary. Contributor trust: 2548 [recommend contributor recommended]. Question popularity: 18 [recommend question].