köken: From 酢(す) (su, “vinegar”) + adjective-forming suffix し (shi), modern い (i). Appears as early as the late Heian period, in the 今昔物語集 (Konjaku Monogatari Shū, “Anthology of Tales from Today and Yesterday”). The spelling with the kanji 酸 is based on synonyms in Chinese: 酢, 醋, and 酸 all have senses related to sour, and all three can be used in Japanese to spell 酢(す) (su, “vinegar”).