slick as a whistle
Very-smooth and neat; also, smoothly, quickly, easily. For example, That salesman is as slick as a whistle, or The fence post went in place slick as a whistle. The allusion in this simile, first recorded in 1830, is not totally clear, but presumably it refers either to the ease of producing a whistle or to its clear tone.
Words nearby slick as a whistle
slice bar,
slice of the pie,
slice-of-life,
slicer,
slick,
slick as a whistle,
slicken,
slickenside,
slicker,
slickrock,
slickster