うんこ

A casual, unrefined word for feces. Related to the verb-like grunt うん ('mm, unh') uttered during defecation — the -こ suffix is a common diminutive/childish ending (as in 猫(ねこ) → にゃんこ).

Register

• Strongly casual and childlike. Can sound humorous, unrefined, or vulgar depending on context — fine among close friends or family and unremarkable from a child, but inappropriate in formal, polite, or medical settings.
• In medical or formal settings, use 便(べん) ('stool') or 大便(だいべん) ('feces, bowel movement').
• In mild casual register, うんち is even softer and more childish.

Common collocations

• うんこをする: to poop
• うんこがしたい: to need to poop / feel like going number two
• うんこが出(で)る: to have a bowel movement (plain)
• 犬(いぬ)のうんこ: dog poop
• うんこを踏(ふ)む: to step in poop

Similar words

• うんち: poo/poop — even softer, more childish variant.
• 大便(だいべん): stool/feces — formal, clinical term.
• 便(べん): stool — medical term, used in compounds like 便秘(べんぴ) ('constipation'), 軟便(なんべん) ('loose stool').
• 糞(くそ) / 糞(ふん): dung/excrement — also used as a swear word ('damn/shit') in the reading くそ.

Notes on writing

• Written in hiragana (うんこ) most often, sometimes in katakana (ウンコ) for comic or emphatic effect.
• No standard kanji.