Get offa me.
Dear Word Detective: What’s the origin of “piggy back” as in, “I’ll just piggy back my new process onto your existing process”? It seems to imply that by piggy backing, you can take a shortcut, particularly by using something that has already been created. — Doug Phillips.
Well, that’s strange. I knew for a fact that I had written about “piggyback” (usually treated as one word) years ago, but when I checked my archive page, it wasn’t there. After tearing out about ten percent of my hair, I finally realized that I had actually written about “piggyback” for a children’s word-origins book. (Which is, as yet, unpublished. If anyone’s interested, drop me a line. We’ll do milk and animal crackers.) But something tells me that you’re not looking for an explanation that begins “One of the coolest things you can do when you’re a little kid is to get a grownup to give you a piggyback ride. You get to see what it’s like to be a lot taller, and you also get to find out how fast grownups can run when you shout ‘Giddyup!’ in their ears.”
Your mention of “process” in your question leads me to suspect that you are a computer programmer or software engineer, and that “piggybacking” in your field means using code that is already in place rather than beginning from the dreaded square one. But “piggyback” in that sense is a metaphorical extension of the literal meaning of “to carry something, especially another person, on one’s back.”
“Piggyback” has been around for quite a while, since at least the 16th century, and, as the Oxford English Dictionary puts it, “the expression has clearly been analyzed in many varying ways from a very early date” (translation: “many theories, no clear answer”). The earliest forms of the term, including “pick pack,” “pick back” and “pick-a-pack,” make no mention of pigs, so we can assume the bacon came later. The common element in these early forms, “pick,” is an old English dialect word related to “pitch” meaning “to throw or place” (as we “pitch a tent” today). The “pack” was most likely the load carried, whether inert or human, so “pick-a-pack,” for instance, might mean to “pick (put) the load on the bearer’s back.” The use of “back” in some early forms reinforces this interpretation.
By the 18th century, “pickaback” had become the dominant form, but there was a problem. The “back” part was clear, but no one at that point understood where the “picka” came from. So through a process fairly common in language known as “folk etymology,” people replaced the part of the word that made no sense (“picka”) with one that sorta, maybe, kinda did (“piggy”). Voila, “piggyback.” Of course, it didn’t really make sense, since pigs would vigorously resist transport in such fashion, but at least it sounded like normal English.
Figurative uses of “piggyback” are fairly recent, dating back just to the 20th century, and most of those have involved carrying one thing on another (e.g., trucks on flatbed railway cars).