(a)smoothhaving a surface free from roughness or bumps or ridges or irregularities“smooth skin”, “a smooth tabletop”, “smooth fabric”, “a smooth road”, “water as smooth as a mirror”
(s)politic, smooth, suave, blandsmoothly agreeable and courteous with a degree of sophistication“he was too politic to quarrel with so important a personage”, “the manager pacified the customer with a smooth apology for the error”
(s)fluent, fluid, liquid, smoothsmooth and unconstrained in movement“a long, smooth stride”, “the fluid motion of a cat”, “the liquid grace of a ballerina”
(s)placid, quiet, still, tranquil, smooth, unruffled(of a body of water) free from disturbance by heavy waves“a ribbon of sand between the angry sea and the placid bay”, “the quiet waters of a lagoon”, “a lake of tranquil blue water reflecting a tranquil blue sky”, “a smooth channel crossing”, “scarcely a ripple on the still water”, “unruffled water”