Dear Word Detective: What does the phrase “light somewhere” come from? My mom used to say it when she wanted someone to sit down and quit moving around. — Taylor Leigh.
I’m going to play psychic here for a moment and hazard a guess (which is what professional psychics do, after all) that you grew up in the American South or southern Midwest. I’m not really psychic, of course, but those are the regions of the US where you’re most likely to hear “light” used to mean “sit down,” according to the Dictionary of American Regional English (DARE).
The first thing to note about “light” is that there are two entirely separate verbs “to light” in English, words which, although spelled the same, have absolutely no connection to each other. The one we needn’t worry about at the moment is “light” meaning, generally, “to give or shed light” or “to set burning.” This “light” (and the noun form meaning “illumination”) comes from the same Indo-European root that produced the Latin “lux” (light), which gave us “luminous,” “lucid,” “illuminate” and other common English words, including “Lucifer,” which means literally “bearer of light.”
The other “light,” the relevant one, comes from a Germanic root with the general sense of “not heavy,” which is how we use the adjective today (as in “many hands make light the load”). As a verb, “light” followed an odd course. In Old English, “to light” meant simply “to lessen the weight of something,” a sense carried over to modern English and elaborated into meanings ranging from “make cheerful” to “give birth,” all of which are obsolete today. One variant of the “make less heavy” use of “to light” did survive in the phrase “to light out” meaning “to quickly leave,” which came from seamen “lighting,” or working together (“making light the load”), to hoist sails. This is also the source of “to light into,” meaning “to begin quickly” or “to attack fiercely.”
The other general sense of “to light” is “to descend, to step down” (essentially the same word as “alight”). The original meaning of this “to light” was “to dismount from a horse or descend from a carriage,” which seems very odd until you realize that dismounting from a horse lightens the load on the horse. This “to light” developed a number of senses based on the general notion of descending, from “to light upon” (“to chance or stumble upon” an idea, for instance) to “light” meaning “to fall or settle on a surface” as a bird or a snowflake might. This last sense, to alight and sit still as a bird might, is the one your mother was using.