The origin of this word is mysterious。 Some people say that the name `Chipangu' used by Marco Polo is not the origin of `Japan'。
They claim that "Japan" came from Malaysian `Jih-pun' or something similar, which came from the southern Chinese dialect reading of Nippon。
Others say that when Marco Polo visited China, Chinese pronunciation was close enough to modern Mandarin that the character for "day/sun" was a retroflex fricative, something like the "Z" in "Zaza Gabor," or "j" and "r" pronounced simultaneously and held for a syllable。
The character for "origin/root/bookscroll" was read something like "pun" (as in modern Mandarin, though it sounds more like the English word "bun" to English speakers), so Marco Polo did the best he could in Italian with what sounded to him like "jrjrrrpun"。
The weakest part of this account is the attribution to M。 Polo; perhaps it was somebody who came along later?
来个汉语的解释：
Japan，「日本国」的福建话发音是：Jih-pen-kuo，到了唐代把国（kuo）省略掉，成了Jih-pen。
而马可波罗在游记中将日本记载为Zipangu。传回欧洲，后来透过罗马文字表记酿成了今天的Japan。