油断

Japanese

Alternative spelling
油斷 (kyūjitai)

Unclear, with multiple theories.

From the story of the 油鉢 (yuhatsu, “pot of oil”) in the Mahāparinirvāṇa Sūtra (大般涅槃経); see 大般涅槃経#油断大敵.
譬如世間有諸大眾，滿二十五里。王敕一臣持一油缽，經由中過，莫令傾覆。若棄一滴，當斷汝命。 [Classical Chinese, trad.]
譬如世间有诸大众，满二十五里。王敕一臣持一油钵，经由中过，莫令倾覆。若弃一滴，当断汝命。 [Classical Chinese, simp.]
Pìrú shìjiān yǒu zhū dàzhòng, mǎn èrshíwǔ lǐ. Wáng chì yī chén chí yī yóubō, jīngyóu zhōng guò, mò lìng qīngfù. Ruò qì yī dī, dāng duàn rǔ mìng. [Pinyin]
For example, in our world there is a large crowd, filling 25 li. The king ordered a minister: "Carry a pot of oil and pass through the crowd; do not let it tip. If a single drop falls out, your life shall end."
Sound change from 寛(ゆた)に (yuta ni).
There is a lamp in Enryaku-ji (延暦寺) that has been alight since the time of Saichō (最澄), its founder, and 油断 (literally “oil + end”) refers to not letting it go out.

The term is not understood in other parts of the Sinosphere.

油(ゆ)断(だん) • (yudan)

油(ゆ)断(だん)する • (yudan suru) suru (stem 油(ゆ)断(だん)し (yudan shi), past 油(ゆ)断(だん)した (yudan shita))

to be caught off-guard; to be unprepared
油断(ゆだん)するな
yudan suruna
don't let [me, them, …] catch you off-guard; keep your guard up; stay alert

Conjugation of "油断する" (See Appendix:Japanese verbs.)

Stem forms
Imperfective (未然形)	油断し	ゆだんし	yudan shi
Continuative (連用形)	油断し	ゆだんし	yudan shi
Terminal (終止形)	油断する	ゆだんする	yudan suru
Attributive (連体形)	油断する	ゆだんする	yudan suru
Hypothetical (仮定形)	油断すれ	ゆだんすれ	yudan sure
Imperative (命令形)	油断せよ¹ 油断しろ²	ゆだんせよ¹ ゆだんしろ²	yudan seyo¹ yudan shiro²
Key constructions
Passive	油断される	ゆだんされる	yudan sareru
Causative	油断させる油断さす	ゆだんさせるゆだんさす	yudan saseru yudan sasu
Potential	油断できる	ゆだんできる	yudan dekiru
Volitional	油断しよう	ゆだんしよう	yudan shiyō
Negative	油断しない	ゆだんしない	yudan shinai
Negative continuative	油断せず	ゆだんせず	yudan sezu
Formal	油断します	ゆだんします	yudan shimasu
Perfective	油断した	ゆだんした	yudan shita
Conjunctive	油断して	ゆだんして	yudan shite
Hypothetical conditional	油断すれば	ゆだんすれば	yudan sureba
¹ Written imperative ² Spoken imperative