n.
1.any very difficult 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
Idiom of the Day
go in for (something)
to choose something as one's particular interest, to occupy oneself with something
My friend is going to university and will go in for medicine. Many of the students are going in for water sports recently.