Other forms: jabbering, jabbers
To jabber is to talk fast and unintelligibly. A stream of sound with no gaps in it.
The word carries the listener's frustration in it, since jabbering is what other people's speech sounds like when you cannot follow it. That makes it worth using carefully, because it has often been applied to languages the speaker simply did not understand. As a noun it means that same rapid noise. Its close relatives are gabble and babble, and all three are imitative words built out of the sound they describe.
1verbjabberTo talk rapidly and in a way that cannot be understood.
“Two men were jabbering into their phones.”
Jabber is jaw-work. Middle English chaveren meant to chatter or babble, built on chavel, a jaw, which is the word that later became jowl.
Middle English
jaberen
English, today
jabber
Built from
From Middle English jaberen, javeren, chaveren (“to chatter, babble”), dissimilated forms of jablen, chavelen (“to jabber”), from Middle English chavel "jaw"; > modern English jowl. Equivalent to jowl + -er.
Etymology from Wiktionary, CC BY-SA