Gibbered, past participle of gibber. Synonyms in the same form.
Prattle
prattled, palavered, piffled, gabbled, prated, talked, chattered, waffled, clacked, blabbed, mandered, twaddled, tittle-tattled, blabbered, tattled, grabbled, gossiped, rambled, gabbed, babbled, clattered
Other
stammered
All synonyms for gibber →