crucial [E18th] The Latin word crux, ‘a cross’, is the source for crucial. It was originally a technical term, especially in anatomy, meaning ‘cross-shaped’, and a close relative appears in the name of the knee’s cruciate ligament [L19th]. The meaning ‘decisive’ or ‘very important’, as in ‘at a crucial stage’, can be traced back to the Latin phrase instantia crucis ‘crucial instance’, coined in the early 17th century by the English statesman and philosopher Francis Bacon (1561–1626). His metaphor was based on the idea of a signpost at a crossroad—a place where you have to choose which way to go next. See also cross, excruciating.