Complexity rhymes with:
perplexity, perplexity, perplexity, laxity, perplexity, analyticity, animosity, atrocity, audacity, biodiversity, capacity, complicity, curiosity, density, diversity, domesticity, eccentricity, elasticity, electricity, falsity, felicity, ferocity, generosity, incapacity, intensity, laxity, monstrosity, necessity, obesity, opacity, overcapacity, paucity, perplexity, perversity, publicity, religiosity, simplicity, specificity, toxicity, university, velocity, viscosity, voracity
Complexity sounds like:
camouflaged, complicate, complicated, complicit, complicity, conflict, conflicted