means A pledge is a solemn, binding promise to do something or to give something, often offered as a guarantee of good faith.

from From the Old French 'plege' or 'plige,' meaning a surety or hostage given as security — itself likely rooted in a Frankish word related to guaranteeing or vouching. The earliest pledges were uncomfortably literal: a person handed over, or goods left behind, as living proof you'd keep your word. Over centuries the hostage faded and only the promise remained, though the old weight still clings to the word.