Words at Play : Top 10 Rare & Amusing Insults, Vol. 2
Definition:
a person who talks foolishly at length
About the Word:
It's alteration of the Scottish compound blather skate (skate means "a contemptible person").
The word appears in a mid-seventeenth century Scottish ballad called Maggie Lauder in which the fair maiden bids her would-be suitor, "Begone ye hallanshaker / Jog on your gait, ye blatherskate ..." [Get lost, you vagabond / Be on your way, you blatherskate ...].