appeal. In British English, if someone appeals against a legal decision or sentence, they formally ask a court to change the decision or reduce the sentence. He appealed against the five year sentence he had been given. Speakers of American English do not use 'against' after appeal.They say that someone appeals a decision.. appeal - (law) a legal proceeding in which the appellant resorts to a higher court for the purpose of obtaining a review of a lower court decision and a reversal of the lower court's judgment or the granting of a new trial; their appeal was denied in the superior court.