欠ける
かける · kakeru · JLPT N3 · verb-ichidan
to be lacking
🍰🌙 kakeru sounds like cake-ru: a cake lacking a slice is 欠けている
欠 is the lack radical, also in 欠席 (absent from a seat) and 欠点 (a flaw). 欠ける covers a chipped cup, a waning moon (月が欠ける) or a team that is one person short. In each case a piece is missing from something that should be whole.
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).