1. Impossible to achieve
   - unattainable, undoable, unrealizable, unrealisable [Brit]

See also: impossible, unachievably

• irrespective
• irresponsibility
• irresponsible
• irresponsibleness
• irresponsibly
• irresponsive
• irretrievable
• irretrievably
• irreverence
• irreverent
• irreverently
• irreversibility
• irreversible
• irreversible process
• irreversibly
• irrevocability
• irrevocable
• irrevocableness
• irrevocably
• irrevokable
• irridenta
• irridentism
• irridentist
• irrigate
• irrigation