Several parts combine into one character.

In oracle bone script, 九 originally pictured a bent arm at the elbow — the meaning was "elbow / bent". Phonetic loan repurposed it to write the number nine, and the body part eventually moved to 肘 (elbow). The hooked stroke in modern 九 still traces the bent-elbow shape. Identical across 繁體 / 新字体 / 简体.

Cultural note — the imperial number. As the largest single digit before rolling over to 10, 九 traditionally represents "the maximum / complete / supreme". Imperial Chinese architecture is saturated with 9: the Forbidden City has 9,999 rooms by tradition, the gates have door-knobs in 9×9 = 81 grids, the imperial robes were embroidered with nine dragons. 九重 (jiǔchóng, "ninefold") was a synonym for the imperial palace. The Mandarin homophone with 久 (jiǔ, "long-lasting") strengthens the auspicious sense — wedding gifts of 99 or 999 wish the couple "long love".

In Japanese, 九 has the opposite cultural valence: the on-reading ク (ku) is identical to 苦 (ku, "suffering"), making 9 mildly inauspicious. Some hospitals avoid room number 9. This split — auspicious in China, inauspicious in Japan — is one of the cleanest examples of how the same character carries different cultural weight across the CJK sphere.

Mandarin: jiǔ, dipping 3rd tone. 九月 (jiǔyuè, September), 九十 (jiǔshí, ninety), 九尾狐 (jiǔwěihú, nine-tailed fox — the kitsune-yokai of East Asian folklore).

Japanese: on-readings キュウ (kyū) — 九月 (kugatsu, September — note: irregular reading shifts to ku!), 九時 (kuji, nine o'clock), 九人 (kyūnin, nine people). Kun-reading ここの (kokono) in 九つ (kokonotsu, nine items), 九日 (kokonoka, ninth day of month — high-frequency irregular). The double readings are pure pain for learners.

Financial form: 玖 prevents alteration.

Memory aid: a hooked stroke + diagonal — a bent arm reduced to two strokes.