Definition of "Piggyback" :

noun: the act of carrying something piggyback

verb: bring into alignment with

"An amendment to piggyback the current law."

verb: support on the back and shoulders

"He piggybacked her child so she could see the show."

verb: haul by railroad car

verb: haul truck trailers loaded with commodities on railroad cars

verb: ride on someone's shoulders or back

adverb: on the back or shoulder or astraddle on the hip

"She carried her child piggyback."

adverb: on a railroad flatcar

"The trailer rode piggyback across the country."