adverb

1. on the shoulders or back to carry a child piggyback
2. by a piggyback transportation system
3. so as to be fixed to, carried by, connected with, or dependent on something else

Etymology: alt. of pickaback

adjective

1. on the shoulders or back to give a child a piggyback ride
2. of a transportation system in which truck trailers are carried on flatcars
3. fixed to, carried by, connected with, or dependent on something else a local piggyback tax on top of the state sales tax

transitive verb

1. to carry or transport piggyback
2. to place on or upon in piggyback fashion piggyback a new tax on the current one

intransitive verb