The Collaborative International Dictionary of English v.0.48:

Smoothly \Smooth"ly\, adv.
   In a smooth manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

smoothly
    adv 1: with no problems or difficulties; "put the plans into
           effect quickly and smoothly"; "despite of some mishaps,
           everything went swimmingly" [syn: smoothly,
           swimmingly]
    2: in a smooth and diplomatic manner; "`And now,' he said
       smoothly, `we will continue the conversation'"

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "smoothly":
   ardently, artfully, astutely, cagily, calmly, cannily, cleverly,
   cunningly, easily, effectively, effortlessly, eloquently, evenly,
   expressively, facilely, fervently, flatly, fluently, forcefully,
   foxily, freely, glibly, glowingly, graphically, guilefully,
   hands down, impressively, in glowing terms, insidiously, knowingly,
   lightly, like clockwork, like nothing, meaningfully, no sweat,
   on easy terms, on the sly, on wheels, passionately, peacefully,
   placidly, powerfully, quiescently, quietly, readily, regularly,
   shiftily, shrewdly, simply, slick, slyly, smooth, spiritedly,
   still, stilly, strikingly, subtilely, subtlely, swimmingly,
   tellingly, tranquilly, trickily, uniformly, unperturbedly,
   vehemently, vigorously, vividly, warily, warmly, well, wilily,
   without difficulty