Onyx rhymes with:
audiotronics, avionics, centronics, conics, diasonics, electronics, electronics', endotronics, endotronics', fibronics, flextronics, harmonics, histrionics, ionics, lasersonics, lumonics, microelectronics, mnemonics, nucleonics, personics, philharmonic's, phonics, photronics, plantronics, respironics, sconnix, siliconix, sonics, tectonics, tektronix, telectronics, telephonics, tonics, vitronics
Onyx sounds like:
oehmens, ohioans, ohm's, ohms, ohnemus, omaha's, omans, omega, omens, ominous, onassis, onassis', onassis's, once, one's, oneness, oneok, ones, ones', onex, onex's, ong, onions, onishi, ons, onus, ounce, ounces, owen's, owens, owens's, owing, owings, owning, owns