word square vs mystifier

word square and mystifier both are nouns.

Word	Noun	Adjective	Verb	Adverb
word square	Yes	No	No	No
mystifier	Yes	No	No	No

As nouns, mystifier is a hypernym of word square; that is, mystifier is a word with a broader meaning than word square:

word square: a puzzle where you fill a square grid with words reading the same down as across
mystifier: a particularly baffling problem that is said to have a correct solution

Other hypernyms of word square include puzzle, puzzler, teaser.

word square (noun)	mystifier (noun)
a puzzle where you fill a square grid with words reading the same down as across	a particularly baffling problem that is said to have a correct solution