A reader asks about the words fatigable, defatigable, and indefatigable:
Indefatigable apparently is of the same/identical meaning [as defatigable]. Then why is the ‘in’ used as a prefix of defatigable, when ‘in’ is generally used to invert the meaning, as in ‘incorrigible’ (antonym of corrigible)?
The reader says that he understands fatigable to refer to a person “who can be fatigued” and defatigable to a person “who can be treated for exhaustion.”
The reader has misunderstood the meaning of de- in indefatigable.
Note: The pronunciation of indefatigable is IN-duh-FAT-i-guh-buhl.
Fatigable and defatigable mean the same thing. They have Latin equivalents:
fatigare verb: to weary, tire, fatigue.
fatigatio noun: weariness, fatigue.
defatigare verb: to weary, fatigue, tire.
defatigatio noun: exhaustion, weariness, fatigue.
The Latin prefix de- is used with more than one meaning. One of these meanings, in both Latin and in English, is this:
de- (prefix): down to the bottom, completely, thoroughly.
Both fatigable and defatigable connote weariness, but the weariness expressed by defatigable is total exhaustion.
Latin also has source words for the form indefatigable:
indefatigabilis adjective: untiring
indefatigatus adjective: not tired
A Google search produces about 22,000 results for defatigable, 114,000 for fatigable, and 708,000 for indefatigable. The Ngram Viewer shows a marked decline in the use of indefatigable in recent decades.
Here are recent examples of the use of indefatigable on the Web:
Indefatigable drive and charisma have made Maura Healey the state’s attorney general and the one to watch in Massachusetts politics.
To some, millennials— those urban-dwelling, ride-sharing indefatigable social networkers—are engaged, upbeat and open to change. To others, they are narcissistic, lazy and self-centered.
The marigolds are indefatigable. The geraniums are lush and valiant.
The indefatigable Vermont Sen. Bernie Sanders, of course, led the pack.
Indefatigable is the opposite of defatigable and means, “incapable of being fatigued.”