Defraud is defined as to use illegal means or deception to trick someone, usually to obtain money.(verb)
When you lie and say that you are the tax collector in order to trick people into giving you money, this is an example of when you defraud people.
See defraud in Webster's New World College Dictionary
Origin: ME defrauden < OFr defrauder < L defraudare < de-, from + fraudare, to cheat < fraus, fraud
See defraud in American Heritage Dictionary 4
transitive verb de·fraud·ed, de·fraud·ing, de·frauds
Origin: Middle English defrauden
Origin: , from Old French defrauder
Origin: , from Latin dēfraudāre
Origin: : dē-, de-
Origin: + fraudāre, to cheat (from fraus, fraud-, fraud).
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