Meaning

adjective of extreme importance; vital to the resolution of a crisis

adjective having crucial relevance

adjective of the greatest importance

origin1706, from French crucial, a medical term for ligaments of the knee (which cross each other), from Latin crux, crucis (“cross”) (English crux), from the Proto-Indo-European *(s)ker- (“to turn, to bend”). The meaning “decisive, critical” is extended from a logical term, Instantias Crucis, adopted by Francis Bacon in his influential Novum Organum (1620); the notion is of cross fingerboard signposts…

Etymology from Wiktionary, CC BY-SA 3.0