Here's what rhymes with onomastic.
monastic mastic elastic plastic fantastic drastic dynastic inelastic spastic aplastic clastic bombastic nonelastic scholastic neoplastic sarcastic gymnastic thermoplastic orgiastic stochastic periphrastic enthusiastic hyperplastic hypoplastic iconoclastic ecclesiastic viscoelastic unenthusiastic interscholastic overenthusiastic Words that almost rhyme with onomastic
automatic magic gastric lactic manic pneumatic tactic asthmatic fanatic malefic matchstick dramatic classic romantic static fabric hepatic metallic panic semantic aromatic dogmatic emphatic frantic somatic thematic erratic mechanic nomadic rheumatic synaptic cinematic galactic kinematic operatic pedantic phallic magmatic spermatic tannic slapstick dynamic traffic tragic gigantic graphic ceramic climatic pragmatic schematic thoracic traumatic autocratic catholic didactic enigmatic enzymatic lymphatic aliphatic axiomatic chromatic climactic emblematic ophthalmic panoramic achromatic anaphylactic idiomatic italic pelagic satanic syllabic acrobatic unromantic ataxic botanic thermostatic tyrannic undramatic nondramatic unemphatic apparatchik baldric aerobatic democratic organic diplomatic systematic problematic pancreatic symptomatic volcanic barbaric ecstatic hemorrhagic metastatic oceanic sporadic thermodynamic cephalic galvanic messianic monochromatic presynaptic prismatic programmatic thalamic tympanic haemorrhagic muriatic phlegmatic theocratic titanic zygomatic bimetallic nonmetallic schismatic astigmatic neoclassic numismatic panchromatic stigmatic sycophantic priapic demographic geographic psychiatric inorganic asymptomatic charismatic ethnographic pediatric prophylactic prostatic geriatric glutamic melodramatic nostalgic pornographic psychosomatic topographic transatlantic diagrammatic heraldic holographic intrahepatic orthostatic psychopathic splanchnic technocratic undemocratic unsystematic antidemocratic epigrammatic isobaric paediatric anticlimactic biographic calligraphic intergalactic osteopathic semiautomatic phonographic undiplomatic unidiomatic aristocratic bureaucratic photographic aerodynamic hemodynamic paradigmatic postsynaptic telegraphic angiographic cartographic diaphragmatic homeostatic iconographic intrathoracic lithographic monosyllabic orthographic tomographic unproblematic chiropractic oceanographic stenographic typographic choreographic disyllabic nondemocratic plutocratic photostatic homoeostatic cytoplasmic hydrostatic hypothalamic endoplasmic psychodynamic stratigraphic posttraumatic autobiographic meritocratic polysyllabic transoceanic xerographic seismographic idiosyncratic radiographic chromatographic hydrodynamic electrostatic bibliographic protoplasmic cinematographic crystallographic lexicographic electrocardiographic electroencephalographic