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

See also: noncontroversial, uncontroversial

• slip away
• slip by
• slip carriage
• slip clutch
• slip coach
• slip friction clutch
• slip in
• slip noose
• slip of paper
• slip of the tongue
• slip off
• slip one's mind
• slip ring
• slip road
• slip stitch
• slip-joint pliers
• slip-on
• slip-up
• slipcase
• slipcover
• slipknot
• slipover
• slippage
• slipped disc
• slipper