1. Immune to attack; incapable of being tampered with
   - impregnable, inviolable, secure, strong, unassailable

See also: invulnerable

• know nothing
• know the score
• know what's going on
• know what's what
• know-all
• know-how
• know-it-all
• Know-Nothing Party
• knowable
• knower
• knoweth
• knowing
• knowingly
• knowingness
• knowledgable
• knowledge
• knowledge base
• knowledge domain
• knowledge economy
• knowledgeability
• knowledgeable
• knowledgeableness
• knowledgeably
• Knowlton's cactus
• known