十日
とおか · tooka · JLPT N5 · noun
days
📅 十日 = ten + day, read とおか: native too (ten) + ka (day counter)
Days 2-10 of the month use old native Japanese numbers plus -ka: futsuka, mikka... tooka. Too is the native word for ten (as in とお), with a long o. Same word covers both a span of ten days and the 10th of the month.
十 — single horizontal 一 + vertical 丨
十 originated as a simple vertical line in oracle bone script, representing the number ten, possibly from a knotted cord used for counting. Over time a horizontal stroke was added, giving the modern cross shape. It has consistently meant 'ten' or 'complete' throughout Chinese history.
日 — pictograph of the sun
日 is a pictograph of the sun, originally drawn as a circle with a dot or stroke inside representing the sun's substance. Over time the round shape was squared off into the modern rectangular form. It means 'sun' and by extension 'day'.