Where does “blabbermouthed” come from?

blabbermouthed (English) comes from English blabber, from Middle English blaberen — to blabber, babble.

blabbermouthed (English): Talkative, especially in an indiscreet manner

Definitions

  1. Talkative, especially in an indiscreet manner

Ancestry of “blabbermouthed”, step by step

blabbermouthed traces back through two separate lines of ancestry.

via English blabber

StepLanguageWordMeaning
1EnglishblabberTo blather; to talk foolishly or incoherently; To...
2Middle Englishblaberento blabber, babble

via English mouthed

StepLanguageWordMeaning
1EnglishmouthedHaving a specified type of mouth; simple past...
Every word from Middle English blaberenEvery word from English blabber