Gordian knot

Từ điển WordNet v3.1 - WordNet Dictionary

noun

1. any very difficult problem;
insoluble in its own terms
• Hypernyms:
problem
2. an intricate knot tied by Gordius, the king of Phrygia, and cut by the sword of Alexander the Great after he heard that whoever undid it would become ruler of Asia
• Hypernyms:
knot