Original: The common name comes from a Portuguese war ship type of the 15th and 16th century, the man-of-war (named caravela-portuguesa in Portuguese, caravel), which had triangular sails similar in outline to the bladder of the Portuguese Man O' War.
Simplified: The common name comes from a Portuguese war ship type of the 15th and 16th century, the man-of-war (named caravela-portuguesa in Portuguese, caravel).