From The Collaborative International Dictionary of English v.0.48 :
blabby \blab"by\ adj. same as blabbermouthed 1. Syn: bigmouthed, blabbermouthed, talkative. [WordNet 1.5]From WordNet (r) 3.0 (2006) :
blabby adj 1: unwisely talking too much [syn: bigmouthed, blabbermouthed, blabby, talkative]