humdinger /hum-dingˈər/ (slang)

1. An exceptionally excellent person or thing
2. A smooth-running engine
3. A swift vehicle or aircraft

• unimaginativeness
• unimagined
• unimbued
• unimmortal
• unimolecular
• unimpaired
• unimparted
• unimpassioned
• unimpeachable
• unimpeached
• unimpeded
• unimpededly
• unimplored
• unimportance
• unimportances
• unimportant
• unimportuned
• unimposed
• unimposing
• unimpregnated
• unimpressed
• unimpressible
• unimpressionable
• unimpressive
• unimprisoned