crux: A cross; a difficulty; a stumbling-block; a puzzle; e.g. crux criticorum, crux mathematicorum, crux medicorum, The puzzle of critics, mathematicians, physicians.
Simply Latin (and a bit of Greek)
crux: A cross; a difficulty; a stumbling-block; a puzzle; e.g. crux criticorum, crux mathematicorum, crux medicorum, The puzzle of critics, mathematicians, physicians.