caltrop (small, metal object with spikes arranged so that, when thrown onto the ground, one always faces up as a threat to pedestrians, horses, and vehicles) · trap, snare (for animals) · pitfall, trap, snare
a pit trap or snare · a hole in the top of a box or other container for dropping things in · a deliberate ploy to deceive someone into a bad situation: a deliberate pitfall
köken: Compound of 落(お)とし (otoshi, “dropping, making something fall”, the 連用形 (ren'yōkei, “continuative or stem form”) of verb 落(お)とす (otosu, “to drop something, to make something fall”)) + 穴(あな) (ana, “hole”). Originally referred to a kind of trap. First attested to the early 1200s.
köken: De Vaan dismisses any relation with Ancient Greek χειά (kheiá, “serpent's den”), and leaves the origin open. He notes that favissae (“underground cellars”) may or may not be related. Older theories derived the word from a Proto-Indo-European *bʰow- (“pit, hole”) (compare Proto-Germanic *būkaz (“belly”)).