Other forms: gibbering
To gibber is to talk fast and unintelligibly from fear. Gibbering with terror, gibber at him, a gibbering wreck.
It is almost always attached to fear or madness, and a gibbering wreck is the fixed phrase. The word is probably a back-formation from gibberish, which came first — so the noun made the verb rather than the other way round.
1verbgibberTo talk fast and unintelligibly from fear.
“The survivor was gibbering with terror and could not explain what had happened.”
gibber is a way of speaking.
Probably a back-formation from gibberish, whose own origin is uncertain and may be imitative.
unknown; usually regarded as a a back-formation from gibberish (see gibberish for more).
Etymology from Wiktionary, CC BY-SA