Dear Word Detective: My love of words and their history has made me a sort of nerdy celebrity among my friends (we are grad students in Environmental Education, so we’re mostly science nerds). Usually when my pals come to me with word queries, I’m able to use a little investigative work (a dictionary and your column, basically) and then stun them with my etymological prowess. Alas, I have been stumped. If “predation” and “depredation” mean the same thing, why do we have the two different words? Why does one have that confusing “de-” prefix? Did they always mean the same thing, or did they diverge at one point? Is “depredation” in any way related to “deprive” instead of “prey”? — Crysta.

Well, lookie there. Signs of intelligent life on Earth. Good to see, because lately I’ve been getting a lot of questions about Sparta, inspired (if that’s the right word) by some silly movie made from a comic book. (Excuse me, “graphic novel.”) Curious, I actually looked up the movie on Wikipedia, and they had posted a big “spoiler warning” before the plot summary because it apparently reveals the super-secret ending of the Battle of Thermopylae. I guess if that’s the sort of thing you like, that’s the sort of thing you wouldn’t know.

“Predation” and “depredation” do mean essentially the same thing in standard usage, “plundering, pillaging, ravaging, exploitation, destruction or ruthless consumption.” Since you and your friends are students in Environmental Education, you are no doubt aware that “predation” is also used in scientific contexts to mean “the preying by one animal upon another; the behavior of a predator,” a usage which lacks the moral judgment implicit in the more general use of the word.

The root of both words, the Latin “praeda,” meaning “booty or prey,” is indeed shared with our English “prey.” This “praeda” begat the Latin verb “praedari,” meaning “to plunder, to rob, to make prey of,” which eventually produced our English “predation” (appearing around 1500) and “depredation” (1626). Neither of these words is related to “deprive,” which harks back to the Latin “privare,” meaning “to isolate or deprive” (also the source of “private,” from the sense of “a single person”).

As to how “predation” and “depredation” can mean the same thing when the prefix “de” usually plays the same negative role as “un” (as in “depopulate”), it’s time to blame those tricky Latin prefixes again. In “depredation,” the prefix “de” means not “un” but “thoroughly, completely,” a role it also plays in words such as “denude” (make completely naked), “declare” (make completely clear), and “despoil” (thoroughly ruin). So “depredation” means “utter, total predation,” damaging or destroying something severely.

Dear Word Detective: Recently, my new hubby and I were discussing what to tile the patio with, and he kept calling it “the floor.” Ever since childhood I have thought that “floor” is for inside, but “ground” is for either. Is either of these right? — Megan.

Well, this just bolsters my theory that home improvement, especially the “DIY” kind (“DIY” standing for “done in years” in most cases), is a leading cause of marital discord today. Just swing by Home Depot or Lowe’s some Saturday afternoon and take a good look at the couples picking out bathroom tiles or window blinds. Do those people look happy with each other? No wonder “home” and “homicide” both begin with “hom.” In fact, your first sentence could pass muster as a classic New Yorker cartoon caption.

I’m not certain I’m the right person to answer your question, since my standard reply to “What’s it like outside?” is “The ceiling is blue and very far away,” but I’ll take a shot.

The use of “ground” outside and “floor” inside is purely a convention, albeit one so old it is nearly universally observed. The only use of “ground” inside a house I can imagine is, perhaps, when the SWAT team kicks in your door shouting, “Get on the ground!”

“Floor” and “ground” are both, as you might suspect, very old words. “Ground” is one of a family of words in various Germanic languages (of which English is one) derived from an ancient Germanic root with the general sense of “very deep place” or “abyss.” When “ground” first appeared in Old English, it meant “bottom, lowest point,” especially the bottom of of the ocean (a sense still found in the phrase “run aground” when the water turns out to be a bit too shallow). “Ground” went on to develop a great varieties of meanings, most focusing on the idea of “foundation” or “surface of the earth,” although we still use the archaic definition “sediment settled from liquid” when we speak of “coffee grounds.” (Surprisingly, calling these “grounds” has nothing to do with the coffee having been put through a grinder. Before filters and similar froo-froo, the coffee was simply stirred and allowed to settle in the bottom of the cup.). But apart from metaphorical uses (e.g., to “stand your ground” in an argument, or “to ground” a fractious child), almost all uses of “ground” in the general “surface” sense take place outdoors.

“Floor” also first appeared in Old English and is based on a Germanic root, in this case carrying the general meaning of “flatness.” Throughout its history in English, “floor” has pretty much been confined to meaning “the level surface underlying the interior of a room” or metaphors invoking that image (as in “floor of the mouth” or “ocean floor”). So “floor” isn’t quite right for a patio, unless it is perhaps somewhat enclosed. If all else fails, I’d just refer to “the surface” of the patio.