expression, i-adjective
indispensable; essential; cannot do without
Fixed expression meaning something is so important that one cannot lack or omit it. Often modifies nouns with な (欠くことができない存在).
水は生きるために欠くことができない。
Water is indispensable for living.
彼はこのプロジェクトに欠く
He is an essential person for this project.