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detailed; full; minute
knowing very well; knowledgeable (about); well-acquainted (with); well-informed (about); familiar (with)
委しい説明のおかげでよく理解できて助かった。
The detailed explanation helped me understand well.
彼は日本の歴史にとても委しい人だ。
He is very knowledgeable about Japanese history.
この分野に委しい専門家を探している。
I am looking for an expert well-versed in this field.