word square vs puzzler

word square and puzzler both are nouns.

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

As nouns, puzzler is a hypernym of word square; that is, puzzler 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
puzzler: a particularly baffling problem that is said to have a correct solution

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

word square (noun)	puzzler (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