köken: Compound of 牛 (ushi, “cow, bull”) + 蛙 (kaeru, “frog”), so named for the way that the mating call of the male resembles the call of a bull. This is probably a calque of English bullfrog, although Japanese sources do not mention this. The kaeru changes to gaeru as an instance of rendaku (連濁). Date of first attestation is unclear. The animal itself is native to North America, and there were…