WordNet (r) 3.0 (2006):
pig-a-back adv 1: on a railroad flatcar; "the trailer rode piggyback across the country" [syn: piggyback, pickaback, pig-a-back] 2: on the back or shoulder or astraddle on the hip; "she carried her child piggyback" [syn: piggyback, pickaback, pig-a-back]