Fadness rhymes with:
badness, madness, sadness, awkwardness, backwardness, badness, baldness, blandness, blessedness, blindness, bloatedness, boldness, coldness, crookedness, discontentedness, farsightedness, fondness, goodness, handedness, hardness, high-spiritedness, kindness, lightheadedness, low-spiritedness, madness, mindedness, nearsightedness, poor-spiritedness, preparedness, public-spiritedness, redness, rudeness, sadness, sandness, shrewdness, soundness, spiritedness, vividness, weirdness, wickedness, wildness
Fadness sounds like:
fading, fathoms, fattening, feeding, feedings, fetting, feuding, fidenas, fiefdoms, fifteens, fitness, fitting, fittings, footing, footings, fthenakis, futons