improver

Concise Oxford English Dictionary © 2008 Oxford University Press:
improve/ɪmˈpruːv/

▶verb

• 1 make or become better.

  ■ (improve on/upon) achieve or produce something better than.

• 2 (as adj. improving) giving moral or intellectual benefit.

– derivatives
improvability noun,
improvable adjective,
improver noun.

– origin C16 (as emprowe or improwe): from Anglo-Norman Fr. emprower, based on OFr. prou ‘profit’.