Green’s Dictionary of Slang

(Irish) talkativeness.

1812		Cobbett’s Wkly Political Register 28 Mar. 14: We should hear nothing come out of his beef-head but odes and sonnets on the reconciliation. The world would be inundated with his sentimental slabber.
1841		Atlas (UK) 20 Mar. 10/2: The language of these peoople [...] is a complete slabber [...] a continual slabbering sound is made.
1993		S. Heaney Midnight Verdict 42: With his legalese and his fancy slabber.