Mistook is a verb. It's the past tense of mistake.
I mistook her for my sister in the dimly lit room.
I mistook her for someone else at the party last night.
he though he knew me, but he mistook me for someone else
Mistook is the past tense of mistake.
Honestly, I think it's an adverb because mistook is a verb but, it can be a adjective to, because, an adjective is a describing word that describes whatever you mistook....
Her misapprehension with the situation caused her to lose friends
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.