crux

the word 'crux' was borrowed directly from latin, where it meant "cross," "torture," or "trouble." in latin, the term 'crux' was used metaphorically to denote a severe difficulty or a pivotal point, much like the decisive moment represented by a crossroad or an ordeal. this figurative sense was fully established in latin rhetorical and philosophical usage before being adopted into english in the early 18th century. the modern english meaning, focusing on the essential or critical point of a matter, evolved directly from this latin metaphorical use, bypassing the literal meaning of "cross" in english.

this word is a loanword from latin, borrowed as a complete lexical unit. it is not productively formed from smaller, recognizable morphemes within modern english spelling.