at one's own discretion; on one's own judgment
Used when someone decides or acts based on their own judgment, often without consulting others. Commonly appears in the adverbial phrase 一了簡に.
彼は一了簡にその計画を進めた。
He proceeded with the plan at his own discretion.
The exact derivation is uncertain; the kanji 一 (one) and 了簡 (idea, thought) suggest a single, personal judgment.