Ostentatious rhymes with:
crustaceous, flirtatious, audacious, capacious, ceraceous, crustaceous, efficacious, fallacious, flirtatious, gracious, hellacious, herbaceous, horatius, ignatius, loquacious, mendacious, perspicacious, predaceous, proteinaceous, salacious, sebaceous, spacious, tenacious, vexatious, vivacious, voracious