pig-a-back

Adverbial pig-a-back has 2 senses

• pig-a-back(r = adv.all) pickaback, piggyback - on a railroad flatcar; "the trailer rode piggyback across the country"
• pig-a-back(r = adv.all) pickaback, piggyback - on the back or shoulder or astraddle on the hip; "she carried her child piggyback"