A person who guesses; especially someone who can make a reasonable prediction from little evidence. (noun)
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Use "guesser" in a sentence
"York, where a second-guesser is merely an apprentice working his way up to the truly good stuff."
"Wired later revealed that the hacker used an automated password guesser to figure out the Twitter admin's password, which was "happiness.""
"As Bruce rightly pointed out, to avoid falling victim to a password guesser users need to make their passwords more complex but with us requiring multiple PINs and passwords to access just one bank account this could get messy."