History of the term Piggyback?

Piggyback derives from the terms "pickpack," "pickback," and even "pick-a-pack," all used in the 17th century to indicate the act of hoisting something onto someone's back for carrying. According to the Random House Word of the Day, most etymologists assume "pick" is a variant of the verb "to pitch," meaning "to throw." "Pack" refers to items meant for carrying.

Piggyback is a textbook case of folk etymology, in which a word is modified to something more common or easily understood when the original term has become obsolete, and thus devoid of meaning.

1838, probably a folk-etymology alteration of pick pack (1565), which perhaps is from pick, a dial. variant of pitch (v.).

http://www.etymonline.com/index.php?term=piggyback

Etymology: alteration of earlier a pick pack, of unknown origin

Date: 1565

http://www.merriam-webster.com/dictionary/piggybac...

Alteration of dialectal pig back, alteration of pickaback, pickback, pick pack : probably dialectal pick, to throw (variant of PITCH2) + BACK1 or PACK1

http://www.answers.com/Piggyback

"ORIGIN mid 16th cent.(as an adverb): although analyzed by folk etymology in various ways from an early date, the word's origin remains obscure."