Implacable means impossible to satisfy, calm, or stop. When something is implacable, it won't be appeased, reasoned with, or turned aside.

An implacable enemy refuses to make peace no matter what compromises you offer. In Moby-Dick, Captain Ahab pursues the white whale with implacable determination: nothing can change his mind or slow his obsession. An implacable storm keeps battering a coastline day after day, refusing to weaken.

Think of it as describing forces or feelings that cannot be softened or satisfied. A student might face an implacable deadline that won't budge no matter how much they plead for an extension. Ancient gods were sometimes described as implacable in their anger, meaning no sacrifice or prayer could calm them down.

When you call someone or something implacable, you're saying there's a relentless, unbending quality to it. An implacable opponent in chess never loses focus or shows mercy. An implacable sense of justice drives someone to pursue what's right no matter the obstacles. The word suggests both strength and inflexibility: implacable forces simply won't be moved.