1. Not open to challenge
   "unchallengeable facts"; "a position of unchallengeable supremacy"

See also: noncontroversial, uncontroversial

• pemican
• pemmican
• Pempheridae
• pemphigous
• pemphigus
• pen
• pen name
• pen nib
• pen pal
• pen up
• pen-and-ink
• pen-friend
• pen-tailed tree shrew
• penal
• penal code
• penal colony
• penal facility
• penal institution
• penalisation
• penalise
• penalization
• penalize
• penally
• penalty
• penalty area