1. Inspiring fear
   "a tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic"
   - formidable, unnerving, doubtable [archaic] 
2. Worthy of respect or honour
   "born of a redoubtable family"

See also: alarming, reputable

• image orthicon
• image scanner
• imager
• imagery
• imaginable
• imaginal
• imaginarily
• imaginary
• imaginary being
• imaginary creature
• imaginary number
• imaginary part
• imaginary part of a complex number
• imaginary place
• imagination
• imagination image
• imaginative
• imaginative comparison
• imaginatively
• imaginativeness
• imagine
• imaging
• imaginings
• imagism
• imago