"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.
Entries linking to gibberish
jabber v.
"talk rapidly and indistinctly," 1650s, spelling variant of Middle English jablen (c. 1400), also javeren, jaberen, chaveren, jawin; probably ultimately echoic. Related: Jabbered; jabbering. The noun, "rapid, unintelligible talk" is 1727, from the verb. Related: Jabberment (Milton).
gibber v.
"speak rapidly and inarticulately," c. 1600, probably a back-formation from gibberish. Related: Gibbered; gibbering.