Same or similar material in other lexica; references at Photius alpha880 Theodoridis. The primary headword is in the accusative singular, evidently quoted from somewhere -- perhaps Euripides, Iphigeneia in Tauris 1444. The secondary one, nominative, comes from Euripides, Andromache 158; see the scholia there, and cf. Latte on Hesychius s.v.
The primary headword (A in LSJ s.v.) comes from the noun ku=ma "wave"; the secondary one (B in LSJ s.v.) from the verb kue/w "I carry in the womb"; but ultimately they are from the same root ku- meaning "swell, bulge." See both LSJ entries at web address 1.
[1] Attested only here and, according to Adler, the Ambrosian Lexicon.