Unassailable/ˌʌnəˈseɪləbl/ Definition 1 of 3Pro Tip 1/2Certain Truth Use 'unassailable' when something is absolutely true beyond doubt. The jury found her alibi unassailable. Pro Tip 2/2Beyond Criticism When something can't be criticized, it's 'unassailable'. Often used in debates or discussions. Her record as a judge is unassailable.