From the New Latin cȳma (“young sprout of a cabbage”, “spring shoots of cabbage”, whence the botanic usage (see cyme); its nominative plural forms include the third-declension cȳmata — whence the English cymata — and the first-declension cȳmae — whence the English cymae and cymæ), from the Ancient Greek κῦμα (kuma) (kūma; “swell”, “wave” (both Ancient Greek compounds and English coinages are usually formed in this sense), “billow”, figuratively “a smothering wave or torrent (of men or, in tragedy, adversity)”, “a waved or ogee moulding”, “cyma” (whence the architectural sense), “fetus”, “embryo”, “sprout of a plant” (whence the relevant Latin senses); its nominative plural form is κύματα (kūmata) — whence the Latin cȳmata and whence, in turn, the English cymata — *κυμαί (kūmai), the first-declension nominative plural form which would give precedent to the Latin cȳmae, does not occur), from κύω (kuō, “I conceive”, “I become pregnant”; in the aorist “I impregnate”).
Most English coinages on this root are formed on its short stem, κυμ- (kūm-); however, the fact that the Ancient Greek etymon only inflects as a third-declension neuter noun has led some writers to prescribe forms that preserve the root’s long stem, κυματ- (kūmat-), for philological reasons (see, for example, the 1903 and 1908 citations of cymatoscope). Nevertheless, forms that do not preserve the long stem are almost invariably more common than those that do, and the Latinate phrases that include cyma, namely cyma inversa, cyma recta, and cyma reversa, show that, when employed as a Latin word, cȳma is treated as a first-declension feminine noun rather than as third-declension neuter consonant-stem noun (inversa, rēcta, and reversa are the feminine forms of the participial adjectives inversus, rēctus, and reversus (Latin grammar requires that adjectives agree in number, gender, and case) and the phrases’ plural forms are cymae inversae or cymæ inversæ, cymae rectae or cymæ rectæ, and cymae reversae or cymæ reversæ, respectively; cyma rectum, which treats cȳma as neuter (rēctum is the neuter form of rēctus), is attested, but it is very rare and its etymologically consistent plural form, *cymata recta, is not attested).
Latin derivations and relations of cȳma include cȳmaticus, cȳmatilis (“of the waves”, “sea- or water-coloured”; as the neuter substantive, cȳmatile, “a bluish garment”; whence the English cymatile), cȳmatium (“an ogee”, “an Ionic volute”; from the Ancient Greek κυμάτιον (kumation); whence the English cymatium), cȳmōsus (“full of shoots”; whence the English cymose and cymous), and cȳmula (“a tender sprout”; the diminutive form of cȳma; whence the English cymule). Ancient Greek derivations and relations of κῦμα (kuma) include κυμαίνω (kūmainō, “I rise in waves”, “I swell”, “I seethe”, “I toss on the waves”, “I am pregnant”), κύμανσις (kūmansis, “undulation”), κυμάς (kūmas, “pregnant woman”), κυματηδόν (kūmatēdon, “like a wave”), κυματηρός (kūmatēros), κυματίας (kūmatias, “surging”, “billowy”; “causing waves”, “stormy”), κυματίζομαι (kūmatizomai, “I am agitated by the waves”, “I toss about like waves”), κυμάτιον (kūmation, “a small cyma”, “the volute of the Ionic capital”), κυματοαγής (kūmatoāgēs, “breaking like waves”), κυματοβόλος (kūmatobolos, “throwing up waves”), κυματοδρομέω (kūmatodromeō), κυματοδρόμος (kūmatodromos, “running over the waves”), κυματοειδής (kūmatoeidēs, “like waves: stormy”), κυματόεις (kumatoeis) (kūmatoeis, poetic for κυματίας (kumatias)), κυματολήγη (kūmatolēgē, “wave-stiller”), κυματοπλήξ (kūmatoplēx, “wavebeaten”, of fish “tossed by the waves”), κυματότροφος (kūmatotrophos, “fed from the sea”), κυματοφθόρος (kūmatophthoros, “plundering by sea”), κυματοφορτίδες (kūmatophortides), κυματόω (kumatoō) (kūmatoō; of the wind “I cover with waves”; in passive constructions, of the land “I am swept by the sea”; in passive constructions, of the sea and, metaphorically, of the air when agitated by the voice “I rise in waves”), κυματωγή (kūmatōgē, “place where the waves break”, “beach”), κυματώδης (kūmatōdēs, “on which the waves break”, “billowy”), κυμάτωσις (kumatōsis) (kūmatōsis; of the tide and, metaphorically, of life “flow”), κυμοδέγμων (kūmodegmōn, “receiving or meeting the waves”), κυμοδόκη (kūmodokē, “wave-receiver”), κυμοθαλής (kumothalēs) (kūmothalēs; of Poseidon “abounding with waves”), κυμοθόη (kūmothoē, “wave-swift”), κυμόκτυπος (kūmoktupos, “wave-sounding”), κυμοπλήξ (kumoplēks) (kūmoplēx; a by-form of κυματοπλήξ (kumatoplēks)), κυμοπόλεια (kūmopoleia, “wave-walker”), κυμορρόον (kūmorrhoon), κυμορρώξ (kūmorrhōx, “breaking the waves”), κυμοτόκος (kūmotokos, “of child-birth”), κυμοτόμος (kūmotomos, “wave-cleaving”), and Κυμώ (Kūmō, “Wavy (a Nereid)”). As demonstrated, there are several Classical precedents, both from Latin and from Ancient Greek, for formations on the short stem (κυμ- (kum-)) of this root, although formations on the long stem (κυματ- (kumat-)) are more common in Ancient Greek; consequently, whereas formations on the long stem may be preferable, especially when combined with other Ancient Greek elements, formations on the short stem are by no means incorrect.