implacable.

Unable or unwilling to be calmed, reconciled, or softened.

Use it for

Words that belong together

• implacable hostility
• implacable opponent

On the page

The old feud had made him an implacable opponent.

Usage notes

Primary category: literary / elevated general. Forms: Comparative more implacable; superlative most implacable when comparison is meaningful. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings. Established modern English lexical item. No separate regional spelling or grammatical inflection entry. Writing functions: character, description. Commonness: moderately common.