From the notion of a mothering vowel mating with a fathering consonant and giving birth to a mora, according to Meiji-era linguists, as in father /k/ + mother あ (/a/) = child か (/ka/). This gave rise to two now obsolete phonological terms boon (母音 mother-sound) ' one of the five morae of the あ行 (agyō, “a-row”), that consists solely of a vowel' and shion (子音 child-sound) 'any of the morae with an onset consonant listed on the 五十音図 (gojūonzu, literally “chart of the fifty sounds”), such as か (ka) or し (shi), but not あ (a) or い (i), and not が (ga), じ (ji) or ぱ (pa)'. Now 母音 means 'vowel' and 子音 means 'consonant'.

From Japanese borrowed to Chinese, Korean and Vietnamese.