月底
yuè dǐ · HSK 4
end of the month
📅 月 = moon/month + 底 = bottom; the bottom (end) of the month
底 means bottom or base, so 月底 is literally month-bottom — the tail end of the month. Compare 年底 (year-end) and 月初 (month-start, where 初 means beginning).
月 — pictograph of crescent moon
月 is a pictograph of a crescent moon, chosen over a full circle to distinguish it from 日 (sun). The inner strokes originally depicted the moon's shadow or markings. As a radical it often relates to the moon, time, or (via a lookalike form of 肉 'flesh') body parts.
底 — 广 (shelter radical) + 氐 (phonetic 'dǐ')
底 is a semantic-phonetic compound. The 广 radical depicts a roofed structure or shelter, suggesting the bottom or base of a building. The component 氐 supplies the sound 'dǐ' and originally meant 'low' or 'base,' reinforcing the meaning. Together they convey 'bottom,' 'foundation,' or 'underneath.'