2. smoothly, without any impediment or obstruction; quietly, pleasantly (chiefly dialect)
from smack (vb. used with adverbial force, as in smack went the whip) + smooth (adj.)
From: The History and Adventures of the Renowned Don Quixote
Translated from the Spanish of Miguel de Cervantes Saavedra
The Second Edition
Volume IV. 1761
Chapter IX. Of Clavileno's arrival, and the conclusion of this protracted adventure.