to have the appearance of being large and important when in reality the subject is small and insignificant. to appear larger than one actually is. in playing cards, it's a hand that is claimed to be the winner but actually is the worst hand on the table.
That banana split turned out to be a real trump as there was not enough ice cream and even the banana was tiny. Playing cards, I claimed a trump while trying to bluff but my hand was so bad that I lost to a pair of two's. The new President turned out to be a real trump.