Send it to Dev Null, Manager of Customer Relations.
Dear Word Detective: I noticed that information sites are always encouraging people to “drop us a line.” Fishing? Phishing? Or just plain friendly? Do you know where the expression “drop me a line” originates? — Margherita Wohletz.
Wow. You’re not going to believe this, but I was cleaning out an old desk in the barn today, and I found your question on a scrap of yellowed paper wedged behind one of the drawers. Looks like you sent it way back in 2008. The raccoons had gotten to it, but I managed to make out the writing by holding it up to a candle flame.
See, I told you you wouldn’t believe me. Hey, I’ve been busy lately. I don’t know how I missed your question back then, but I’m glad I found it, because it’s actually a great topic. I have the sense that the popularity of “drop us a line” has faded a bit in the age of email, but it’s actually, as we shall see, every bit as applicable to email as to postal mail.
Our modern English word “line” is actually the result of a merger of two earlier words, the Old English “line” meaning “cord, rope, series, row” and the Middle English (originally French) “ligne,” meaning “thread, cord, linen thread.” Not surprisingly, the two words had a common source, the Latin “linea,” flaxen, from “linum,” flax.
If the noun “line” were a Swiss Army knife, it would have 75 blades and weigh twelve pounds. The Oxford English Dictionary (OED) entry for “line” goes on close to forever and divides the uses of the word into five main senses, each with numerous particular uses: “cord or string,” including cables, fishing lines, and lines aboard ship; “thread-like mark,” including lines drawn for various purposes, a musical passage, mathematical lines, a political policy (as in “party line”), information (“Get a line on”) and geographical boundaries (“Mason-Dixon Line”); “line” as “applied to things arranged along a (straight) line,” including a row of people or things, railway lines, battle lines, rows of letters in text, and conveyances routinely following a set route (bus lines, airlines, etc.); “line” used to denote “serial succession,” as in “family line,” and “line” meaning “direction or course of movement,” as in a “line” of business, or a “line of credit.” The OED goes on to enumerate more than a dozen compound and combination terms also involving “line,” such as “linebacker” and “line-loss” (electrical leakage). I am in awe of this dictionary entry and I hope I never have to read it again.
Meanwhile, back at your question, I direct your attention to Sense III, subsense 23, “line” meaning “a row of written or printed letters.” Subparagraph (a) therein refers to “One of the rows of letters in any piece of writing,” as in the lines of text making up any printed document. These are the “lines” found in the phrase “to read between the lines,” meaning, as the OED puts it, “to discover a meaning or purpose not obvious or explicitly expressed in a piece of writing.”
Two sections south of there, in subparagraph (d), we hit pay dirt, namely “line” defined as “a few words in writing; often applied to a short letter.” This usage dates back to 1647 (“I … desire a line under your own hand to whom I shall deliver the castle,” H. Markham), and has been in common use ever since. The “drop” part of the idiom “drop a line” is a usage dating back to at least 1769 meaning “To let (a letter or note) fall into the letter-box; hence, to send (a note, etc.) in a casual or informal way.” (OED) (“I will drop a line as often as I can,” John Quincy Adams, 1777).
The practice of dropping mail into boxes at the Post Office or on the street corner is, sadly, fading away today, but the point and click nature of email more than fits the “casual” sense of “drop a line.” And to “drop someone a line” is to stay in touch in a personal, one-to-one sense, where even just a short note can mean far more than just another Facebook “like.”