五十音
ごじゅうおん · gojuuon · JLPT N2 · noun
syllabary
五十音 = five + ten + sound: the 50-sound Japanese syllabary (gojuu-on)
五 is five, 十 is ten, 音 is sound. The chart is a grid of 10 columns and 5 vowel rows (a i u e o), with 46 kana in use today.
五 — two horizontal lines + crossed strokes
五 originally depicted two parallel lines (heaven and earth) with an X between them, representing the interaction of the five elements. Over time it became the standard numeral for 'five.' The ancient form 㐅 (just the X) was later framed by the two lines to distinguish it clearly as a number.
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.