The story
From deer + horn + knife. (martial arts knife): From the shape of the knife resembling deer horns or deer antlers.
Etymology from Wiktionary, CC BY-SA 4.0.
deer horn knife
Today it means: A Chinese martial arts knife resembling two crossed crescents with all outward-facing edges sharpened, and a handle on an inside arc of one of the crescents. The blade allows punching, slashing, and stabbing, as well as using the outward points as guards for defence to catch incoming weapons. Full definition →