MISTAKE, BLUNDER, ERROR, SLIP

 

A MISTAKE, grave or trivial, is caused by bad judgment or a disregard of rule or principle: It was a mistake to argue. 

A BLUNDER is a careless, stupid, or gross mistake in action or speech, suggesting awkwardness, heedlessness, or ignorance: Through his blunde,r the message was lost. 

An ERROR (often interchanged with MISTAKE) is an unintentional wandering or deviation from accuracy, or right conduct: an error in addition. 

A SLIP is usually a minor mistake made through haste or carelessness: a slip of the tongue.