Redoubtable means formidable, and to be treated with respect. A redoubtable opponent, the redoubtable Mrs Hall, redoubtable skill.
It is admiring, which separates it from merely frightening — you call an opponent redoubtable when you rate them. The doubt in it is an old word meaning to fear, not the modern doubt. Note that a redoubt, a small fort, is a different word.
1adjectiveredoubtableFormidable, and to be treated with respect.
“The redoubtable headmistress ran the school for forty years and feared no one.”
redoubtable is a quality of strength.
Old French redouter means to fear greatly, from Latin dubitare, to hesitate. The doubt here means fear.
Proto-Indo-European
*wert-
Proto-Indo-European
*dwi- — apart, asunder; two
Latin
dubitō — to doubt, be uncertain, waver in opinion
Old French
redotable
Middle French
redoutable
Anglo-Norman
redoutable
Middle English
redoutable — worthy of honour, venerable; frightening, terrible
English, today
redoubtable
Built from
The is derived from Late Middle English redoutable (“worthy of honour, venerable; frightening, terrible”), borrowed from Anglo-Norman redoutable and Middle French redoutable, redoubtable, from Old French redotable (modern French redoutable), from redoter (“to fear”) (whence Middle French redoubter, redouter, French redouter) + -able. Redoter is derived from re- + doter (“to doubt; to fear”) (from Latin dubitō (“to doubt, be uncertain, waver in opinion”), probably ultimately from Proto-Indo-European dwi- (“apart, asunder; two”) + bʰuH- (“to appear; to be; to become; to grow”), in the sense of being in two minds). by surface analysis, redoubt + -able. The is derived from the adjective.
Etymology from Wiktionary, CC BY-SA