1. Not capable of being improved on
   - unexceeded, unsurpassed

See also: best

• impractical
• impracticality
• impramine hydrochloride
• imprecate
• imprecation
• imprecatory
• imprecise
• imprecisely
• impreciseness
• imprecision
• impregnability
• impregnable
• impregnably
• impregnant
• impregnate
• impregnation
• impresa
• impresario
• impress
• impressed
• impressibility
• impressible
• impression
• impressionability
• impressionable