to utter or tell unnecessarily, or in a thoughtless manner; to publish (secrets or trifles) without reserve or discretion. And yonder a vile physician blabbing The case of his patient. (Tennyson)
Origin: cf. Oe. Blaberen, or dan. Blabbre, g. Plappern, gael. Blabaran a stammerer; prob. Of imitative origin. Cf. Also blubber, v.