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under (guidance, supervision, rules, the law, etc.)
under (a flag, the sun, etc.); beneath
with (e.g. one blow); on (the promise, condition, assumption, etc. that ...); in (e.g. the name of ...)
(someone's) side; (someone's) location
師の許で技を磨いた。
I honed my skills under a master.
母の許を離れるのはさみしい。
It's sad to leave my mother's side.
厳しい規則の許で働いている。
I work under strict rules.