Smallness rhymes with:
awfulness, coolness, dullness, fickleness, forcefulness, foulness, fullness, gentleness, harmfulness, idleness, illness, peacefulness, playfulness, reasonableness, resourcefulness, stillness, truthfulness, usefulness, wastefulness, wellness, wistfulness, wonderfulness
Smallness sounds like:
scanlon's, schmeling, signaling, signalling, smalling, smelling, smiling, smolensk, smolenski, smolinski, smolinsky, snelling, snellings, somalians, somnolence