蛋

Originally derived from 蜑, a phono-semantic compound composed of:

虫 — semantic component (originally related to creatures or living beings);

延 — phonetic component indicating the sound.

The modern form 蛋 developed as the upper part 延 became simplified into a shape resembling 疋. Originally, 蜑 referred to southern tribes (non-Han peoples), but over time the meaning shifted to egg, likely through association with living organisms and reproduction.
Semantic development: - originally: name of a people or group (蜑); - association with living organisms; - meaning shifted to “egg”; - extended to food and biological terms.

In Korean, 蛋 is rarely used alone, and the word for egg is typically written with 卵 (란).

단백질 (蛋白質) — protein

In Chinese, 蛋 is the standard word for egg, unlike Korean and Japanese, which prefer 卵. It appears frequently in food terminology (cake, mayonnaise, etc.). In informal Chinese, 蛋 can be used in slang expressions, sometimes with a slightly negative or vulgar nuance.
Related characters: 卵 — egg (more common in Korean/Japanese)

雞 — chicken

白 — white (as in egg white, 蛋白)