Think of it as a balance held in other people's minds: how far they are willing to take your word as true. Every kept promise adds to it; one broken one takes a lot away.
From the word’s history
From Latin credere ("to believe") — the same root as credit, credo, and incredible. Credit is trust with money; credibility is trust with words.
credibility 來自拉丁 credere（相信），和 credit（信用）、credo（信條）、incredible（難以相信）同一家。這個親戚關係很有用：credit 是別人願意先借錢給你，credibility 是別人願意先相信你的話——兩個都是「別人對你的信任額度」，都要靠紀錄慢慢累積，也都可能一夕透支。
Wiktionary, "credibility" — from French crédibilité, from Medieval Latin credibilitas, from Latin credibilis (credere "to believe") + -ity.
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
credibilitynoun/kɹɛd.əˈbɪ.ɫɪ.ti/
- 1
A reputation impacting one's ability to be believed.
- After weeks of blowing smoke, her credibility with me was next to nil.
- The inability of Trump's own spokespeople to speak authoritatively on the president's thinking and actions -- a challenge even Trump himself has acknowledged -- has left the White House with an enormous credibility gap, and has tarnished the reputations of many of its most visible spokespeople.
- 2
lawA believability of statements by a witness, as measured by whether the testimony is probable or improbable when judged by common experience.
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。