Phage

Then Phage taught the lesson that trips up almost everyone: it has a Latin twin who means the exact same thing.

"When you want to say eater, English gives you two whole families," Phage said. "Me — the Greek -phage/-phagous — and the Latin -vore/-vorous. A plant-eater is a herbivore (Latin) — you'd almost never say phytophage, though it's technically buildable. A meat-eater is a carnivore (Latin). An everything-eater is an omnivore (Latin)." Phage sighed happily. "The Latin -vore family won the everyday words. I — the Greek -phage — mostly took the science words: bacteriophage, and the eating that cells do. Same meaning, two languages, different neighbourhoods. When you meet an 'eater' word, check which family it's from: -vore/-vorous is Latin and common; -phage/-phagous/-phagy is Greek and science-y."

The creatures found this enormously useful. Now an unknown 'eater' word told them not just what it ate but which world it came from.

Phage saved its favourite surprise for last, and it was a spooky one.

"My root phag hides in a word you'd never suspect," it said. "Sarcophagus. A stone coffin. The root sarco means flesh, and phag means... eat. A sarcophagus is, literally, a flesh-eater — the ancient Greeks believed a certain limestone dissolved a body, so they named the stone box the flesh-eater." The young creatures shivered and loved it. "And esophagus — the tube food travels down — has me hiding in it too: it's built from parts meaning roughly the thing that carries what you eat. So I'm not only in obvious 'eater' words. I'm buried inside coffins and throats. A morpheme goes wherever its meaning is needed — even somewhere macabre."

Phage repeated its one honest rule, the one from when it was young.

"I clip onto a root — a meaning-core — not onto random letters," it said. "Find the root first, then add the appetite. If you try to read -phage onto a piece that isn't a real root, you get nonsense. Radix finds the what. I supply the eats. Together we crack the word; alone, either of us is only half a clue."