the American Ambassador to Japan 美国驻日本大使
the Japanese Ambassador in London [to the Court of St. James's] 日本驻英大使
an ambassador extraordinary 特命大使
an ambassador plenipotentiary 全权大使
an ambassador extraordinary and plenipotentiary 特命全权大使
an ordinary [resident] ambassador 常驻[驻在]大使
a roving ambassador 巡回大使,无任所大使.