"speak rapidly and inarticulately," c. 1600, probably a back-formation from gibberish. Related: Gibbered; gibbering.
Entries linking to gibber
gibberish n.
"rapid and inarticulate speech; talk in no known language," 1550s, imitative of the sound of chatter, probably influenced by jabber. Used early 17c. of the language of rogues and gypsies.