mountebank

(noun)

a person who deceives others, esp. in order to trick them out of their money; a charlatan.

historically, a person who sold patent medicines in public places.

word’s encounter: Bryan Magee’s The Philosophy of Schopenhauer.

word’s use: any mountebank proclaiming complete mastery of the English language would most probably proffer a false meaning for the word mountebank if they were paid to provide its definition.