水蒸気
すいじょうき · suijouki · JLPT N2 · noun
water vapor
💧♨️ 水 (water) + 蒸 (steam, evaporate) + 気 (vapor, air) = water that has turned into vapor
蒸 means to steam or evaporate, so 水蒸気 is water that has evaporated into a gas. The same 蒸 appears in 蒸し器 (steamer), a kitchen tool that cooks with steam.
水 — pictograph of flowing water
水 is a pictograph depicting a stream of flowing water, with the central line representing the main current and the side strokes showing splashing droplets or ripples. In oracle bone script it was drawn even more clearly as a wavy vertical line with branches. It retains its original meaning of 'water' and also serves as a radical, often appearing in the compressed form 氵.
蒸 — grass 艹 + 丞 (phonetic) + fire 灬
Originally depicted plant stalks (艹) being heated over fire (灬), with 丞 providing the sound. The character first meant rising steam from burning hemp stalks used as torches, then broadened to mean steaming food or vapor rising. Modern uses extend metaphorically to 'flourishing' or 'thriving.'