欠く
かく · kaku · JLPT N3 · verb-godan
to lack
🦷 kaku sounds like crack-u: a cracked cup lacks a chip
The kanji 欠 began as a person yawning, mouth wide open, and that open gap became the idea of something missing. 欠く means to chip a piece off or to lack something. Don't mix it up with 書く (kaku, to write).
欠 — person 人 below + open mouth 欠 top (yawning figure)
Pictograph of a person kneeling with mouth wide open, exhaling — originally depicting a yawn or breath. From this came meanings like 'to lack' or 'to owe', as if something is missing or breathed out. It now serves as a radical in characters related to breathing, singing, or desire (歌, 歡, 欲).