Several parts combine into one character.

平 is read variously as a balance scale brought level and even, or duckweed spread evenly on water. Either way "even, flat, calm" is its core sense. The horizontal stroke balanced left and right shows "flatness."

Korean hanja-sound "pyeong": 平和 (pyeonghwa, peace), 平等 (pyeongdeung, equality), 平凡 (pyeongbeom, ordinary), 平面 (pyeongmyeon, a plane), 公平 (gongpyeong, fairness), 平均 (pyeonggyun, average), 水平 (supyeong, level). With 和 seen just above it forms 平和 (peace).

Mandarin: píng, 2nd tone. 平等 (píngděng, equality), 平时 (píngshí, ordinarily), 平安 (píng'ān, safe and sound), 水平 (shuǐpíng, level / standard), 公平 (gōngpíng, fair), 平方 (píngfāng, squared). 水平 (shuǐpíng, level) is a daily Mandarin essential.

Japanese: on-readings ヘイ (hei) and ビョウ (byō), kun たい.ら (taira) and ひら (hira). 平和 (heiwa, peace), 平等 (byōdō, equality — a ビョウ reading), 平気 (heiki, calm), 平日 (heijitsu, weekday), 平仮名 (hiragana). The 平 of Japanese ひらがな (hiragana) means "plain, simplified."

Memory aid: a balance scale brought level — even, flat, and calm.