puzzle vs mull

puzzle and mull both are nouns.

Word	Noun	Adjective	Verb	Adverb
puzzle	Yes	No	Yes	No
mull	Yes	No	Yes	No

As verbs, mull is a hypernym of puzzle; that is, mull is a word with a broader meaning than puzzle:

puzzle: be uncertain about; think about without fully understanding or being able to decide
mull: reflect deeply on a subject

puzzle (noun)	mull (noun)
a game that tests your ingenuity	a term used in Scottish names of promontories
a particularly baffling problem that is said to have a correct solution

puzzle (verb)	mull (verb)
be a mystery or bewildering to	reflect deeply on a subject
be uncertain about; think about without fully understanding or being able to decide	heat with sugar and spices to make a hot drink