Why This Word Matters

Some people seem to run on an engine the rest of us do not have. They keep working when others stop. They maintain their energy and focus long after the point where most people would have given up. English has several words for this quality (tireless, relentless, persistent), but "indefatigable" is the most expressive. Its length and rhythm match its meaning. Saying the word itself takes effort, which feels appropriate for a word about effort that never ends.

What It Means

Indefatigable describes a person who cannot be made tired, who persists in effort without becoming exhausted or discouraged. An indefatigable researcher keeps pursuing leads long after the initial excitement fades. An indefatigable campaigner knocks on doors and gives speeches and shakes hands until the very last vote is counted.

The word implies more than simple stubbornness. Stubbornness can be passive, a refusal to move. Indefatigable energy is active and forward-moving. It is the quality of someone who keeps producing, keeps striving, keeps building. There is an almost superhuman quality to it, which is why the word often carries a tone of admiration or even awe.

"Indefatigable" also tends to describe people rather than things. You would not normally call a machine indefatigable, because machines are expected to run continuously. The word is interesting precisely because it describes a human being who displays a capacity for effort that seems to exceed normal limits.

Where It Comes From

From Latin indefatigabilis, formed from in- (not), de- (entirely), and fatigare (to weary or exhaust). The root fatigare also gives us "fatigue." So "indefatigable" literally means "not able to be entirely wearied out." The word entered English in the early 17th century.

The word has a notable military history. HMS Indefatigable was the name of several Royal Navy ships, the most famous being the battlecruiser that fought at the Battle of Jutland in 1916. The name was chosen to project an image of relentless, inexhaustible power.

How to Use It

  • "The indefatigable volunteers rebuilt the community center in half the time anyone expected."
  • "She was an indefatigable advocate for literacy, establishing reading programs in twelve counties over two decades."
  • "His indefatigable curiosity led him to master five languages and three musical instruments before the age of forty."

Words to Know Alongside

Tireless is the most common synonym and works in all the same contexts, though it lacks the grandeur of "indefatigable." Relentless adds a note of intensity or even aggression to the idea of persistence. Dogged emphasizes stubborn determination, often in the face of obstacles. Languid is a useful antonym, describing a person who is slow, relaxed, and lacking in energy or enthusiasm.