refine

Concise Oxford English Dictionary © 2008 Oxford University Press:
refine/rɪˈfʌɪn/

▶verb

• 1 remove impurities or unwanted elements from.

• 2 make minor changes so as to improve (a theory or method).

• 3 (as adj. refined) elegant and cultured.

– derivatives
refiner noun.

– origin C16: from re- + the verb fine1, influenced by Fr. raffiner.