1. Incapable of being overcome, challenged or refuted
   - impregnable

See also: unconquerable

• counterbore
• counterchallenge
• counterchange
• countercharge
• countercheck
• counterclaim
• counterclockwise
• counterclockwise rotation
• countercoup
• counterculture
• countercurrent
• counterdemonstration
• counterdemonstrator
• counterespionage
• counterexample
• counterfactual
• counterfactuality
• counterfeit
• counterfeiter
• unscientifically
• unscramble
• unscrew
• unscripted
• unscrupulous
• unscrupulously