>i guess tidal wave is a misnomer, but why did people pick that particular misnomer to be changed to a japanese word?

when the international community started studying these things I'd guess that they wanted something unique to the phenomenon and the Japanese already had a word that applied to it specifically? I know that in Hawaii they have Tsunami Watches and Tsunami Warnings, just as we have for hurricanes and tornadoes in the U.S. it hasn't been that long that the cause of these things has been known; previously they were thought to just be big "tidal" waves.