problem vs Gordian knot

problem and Gordian knot both are nouns.

Word	Noun	Adjective	Verb	Adverb
problem	Yes	No	No	No
Gordian knot	Yes	No	No	No

As nouns, Gordian knot is a hyponym of problem; that is, Gordian knot is a word with a more specific, narrower meaning than problem:

problem (noun)	Gordian knot (noun)
a source of difficulty	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
a question raised for consideration or solution	any very difficult problem; insoluble in its own terms
a state of difficulty that needs to be resolved