1. benefactor a person who helps people or institutions
  2. car factory a factory where automobiles are manufactured
  3. scale factor a number used as a multiplier in scaling
  4. prime factor the prime factors of a quantity are all of the prime quantities that will exactly divide the given quantity
  5. perfecter a skilled worker who perfects something
  6. growth factor a protein that is involved in cell differentiation and growth
  7. Pyrrhic victory a victory that is won by incurring terrible losses
  8. Rh factor a blood group antigen possessed by Rh-positive people
  9. prefecture the district administered by a prefect
  10. fudge factor a quantity that is added or subtracted in order to increase the accuracy of a scientific measure
  11. breeder reactor a nuclear reactor that produces more fissile material than it burns
  12. calefactory serving to heat
  13. Hageman factor coagulation factor whose deficiency results in prolongation of clotting time of venous blood
  14. cofactor a substance (as a coenzyme) that must join with another to produce a given result
  15. nuclear reactor (physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements
  16. multiplier factor the number by which a multiplicand is multiplied
  17. malefactor someone who has committed a crime
  18. perfectly in a perfect or faultless way
  19. refectory a communal dining-hall, usually in a monastery
  20. provocateur a secret agent who incites persons to commit illegal acts