Here's what rhymes with planktonic.
tonic chronic ionic sonic conic phonic bionic ironic tectonic chorionic colonic demonic iconic mnemonic monotonic platonic daemonic acetonic sardonic ganglionic isotonic laconic synchronic catatonic diatonic subsonic avionic electronic embryonic harmonic hegemonic supersonic diachronic hypertonic polyphonic symphonic architectonic telephonic hydroponic monophonic ultrasonic histrionic infrasonic quadraphonic quadrophonic pathognomonic stereophonic philharmonic microelectronic Words that almost rhyme with planktonic
atomic comic anatomic genomic economic autonomic diatomic uneconomic ergonomic tragicomic agronomic subatomic taxonomic gastronomic astronomic macroeconomic microeconomic socioeconomic topic boric logic toxic chaotic folic gothic tropic anabolic atopic biotic bardic hayrick rollick cosmic aortic aquatic erotic exotic garlic neurotic caloric caustic melodic carbolic idiotic necrotic pyloric cathodic formic frolic gnostic iambic karmic meiotic meteoric myopic robotic thrombotic cirrhotic seraphic strophic subtopic chopstick carsick shambolic placekick historic symbolic alcoholic metabolic periodic antibiotic apostolic hydraulic biologic despotic diastolic episodic geologic hypnotic narcotic prognostic psychotic systolic ascorbic isotopic metaphoric parabolic phenolic agnostic anarchic anoxic basaltic catabolic cathartic dialogic euphoric fibrotic hypoxic melancholic nontoxic sclerotic telescopic antarctic bucolic diabolic folkloric homoerotic acrostic ecologic gyroscopic heartsick rhapsodic allegoric noncaloric gynaecologic diagnostic patriotic prehistoric isotropic neurologic pathologic philanthropic anisotropic etiologic hyperbolic metamorphic psychologic semiotic spasmodic symbiotic synoptic yardstick lethargic orthodontic pedagogic psychotropic quixotic demagogic hierarchic unpatriotic vitriolic xenophobic subarctic workaholic macrobiotic theosophic subtropic chocoholic shopaholic astronautic chocaholic microscopic hydrochloric philosophic catastrophic cytotoxic histologic macroscopic endoscopic immunologic morphologic gynecologic hematologic oligarchic peristaltic polymorphic stereoscopic arthroscopic microcosmic misanthropic posthypnotic sophomoric nonnarcotic aetiologic haematologic seismologic horologic physiologic anthropomorphic atherosclerotic pharmacologic fluoroscopic kaleidoscopic antispasmodic nonalcoholic stroboscopic meteorologic epidemiologic spectroscopic bacteriologic submicroscopic electroscopic