馬ば背はいMeanings1nounhorse's backrare termRare term for the back of a horse. In modern Japanese, 馬の背 (うまのせ) is the usual expression.古ふるい文ぶん献けんに「馬ば背はいに揺ゆられて」という表ひょう現げんが見みられる。In old texts, you can find the expression 'swaying on the horse's back'.