宣誓英语的表达方式是“to swear an oath”或者“to take an oath”。它的来源可以追溯到古希腊和罗马时期，当时人们通常会在宣誓时握着圣经或其他圣物。例如：

I swear to tell the truth, the whole truth, and nothing but the truth. (我宣誓说实话，全实话，不掺杂虚谎。)

She took an oath to serve her country with honor. (她宣誓要以荣耀的精神为国服务。)

希望这些信息能够帮到您。