[ Wiktionary : ] Etymology
From the Ancient Greek κῦμα (kûma), from κύω (kúō, “I am pregnant, I conceive”).
*κυμαί (*kumaí), the first-declension nominative plural form which would give precedent to the Latin cȳmae, does not occur.
- a young sprout of a cabbage
- hollow sphere
- spherical layer, stratum
- spring shoots of cabbage
What underlying semantic notions connect:
'cabbage shoots or sprouts' (1 and 4) to 'hollow sphere' (2)?
Cabbage shoots do not appear spherical; a cabbage does (but which this noun does not mean).
'stratum' (3) to all the other meanings?