Cloud-cuckoo-land: An idealized fantasy world: this term is a translation of the name for an imaginary city, floating in the air in the play The Birds by Aristophanes.
Cutting the Gordian knot: Solving a problem by taking prompt and extremely bold or unconventional action: The phrase is based on a supposed incident that occurred in ancient history. The Gordian knot was an enormous and intricate knot tied with rope made of bark by King Gordius of Phrygia in the 4th century BC. According to the oracle, whoever could undo the knot was destined to reign over a large empire in Asia Minor. Alexander the Great apparently took up the challenge by simply hacking through the knot with his sword in 334BC.
Curate’s egg: Something that is actually bad although claimed by some-out of sensitivity or some other reason – to have both good and pad parts. The phrase derives from a punch cartoon in which a nervous young curate at a bishop’s table is given what is obviously a bad boiled egg but fearful of giving offence tells his host that ‘parts of it are excellent.
This term is often misused. It correctly refers to something which is in fact completely bad or which cannot be redeemed, and not to something which has both good and bad qualities.