From Piglet to Wilbur to Babe to Animal Farm, pigs play a certain minor (or possibly mid-range) role as characters in English writing. Pigs have been domesticated for many centuries, and they’ve entered the language as well.
The thing is, most pig-related words and idioms don’t seem particularly kind to the pigs. The word “hogwash,” meaning nonsense, comes from the kitchen scraps generally fed to pigs back on the farm. Even though pigs are quite intelligent, we use “pigheaded” to describe someone who is (at least) stubborn, and we often mean kind of stupid too. A messy room is a “pigsty” — except left to their own devices, pigs keep themselves quite clean. Buying a “pig in a poke” means getting swindled. The actual origin of that phrase is supposedly true; it was a scam in which a cat was put in a bag (a “poke”) and the seller claimed it was a little pig. If the buyer was too lazy, in too much of a rush, or got talked out of checking inside the bag, they wound up losing their money. Incidentally, you’ve heard the phrase “let the cat out of the bag?” Same cat, same bag.
But there’s one (slightly) pig-related English word that describes something very nice: “porcelain.” You wouldn’t think pigs would be associated with fine china — even though it’s a bull, not a boar, who makes a mess in a china shop in that other old phrase. But in any case, “porcelain” comes from the French word “porcelaine.” That, in turn, was borrowed from the Italian word “porcellana.” “Porcellana,” in Italian, originally had two meanings: fine china and also a seashell. The shell was a “cowrie;” a small, shiny shell found in the Indian Ocean. The name of the shell predates the use of “porcellana” for fine china. It was applied to the plates because their shiny finish reminded people of the shells. As for the shells, they were called “porcellana” because the Italian word for “young pig” is “porcella,” and cowrie shells were said to resemble a small pig. You probably have to squint and hold your head at an angle to see it. By the way, all this loopy linguistic legerdemain occurred around the 1500s when Portuguese ships returned from China carrying shiny ceramics. That’s why porcelain is called “china;” that’s where it was originally from.
There are a couple of other pig-related words in English that are at least neutral: “porcupine” (spiny pig, from the Latin “porcospinus”) and “porpoise” (“pork fish,” from the Old French “porpais” — it was probably based on the observation that the nose of a porpoise is a little bit like a pig’s snout).
And finally there’s “piggyback.” It’s a fairly old word, from the 1500s or so, and although its origin isn’t clear it doesn’t seem to really be related to pigs. It used to be “pickaback,” because “pick,” in several English dialects at the time, meant to throw or place. A modern version would be “pitch a tent.” “Pick-a-back” or “pick-a-pack” would mean to put something (a pack) on someone’s back. By the 1700s the word “pick” had pretty much disappeared, so when people used the (still current at that time) word “pickaback,” at least some of them apparently thought “wait, this makes no sense; it must be a mispronunciation of something else.” (Those people were obviously laboring under the misconception that English makes any sense at all.) But it’s possible that somebody had noticed that baby pigs sometimes jump on each others’ backs when playing (this isn’t unique to pigs, but “pig” sounds pretty similar to “pick”), and concluded that all that time they’d been trying to say “piggyback” but getting it wrong. Enough people agreed with this that by the 1800s “pickaback” had turned into “piggyback” even though it really had been “pick” and not “pig” to start with (probably).