The Collaborative International Dictionary of English v.0.48:

Coefficient \Co`ef*fi"cient\, n.
   1. That which unites in action with something else to produce
      the same effect.
      [1913 Webster]

   2. [Cf. F. coefficient.] (Math.) A number or letter put
      before a letter or quantity, known or unknown, to show how
      many times the latter is to be taken; as, 6x; bx; here 6
      and b are coefficients of x.
      [1913 Webster]

   3. (Physics) A number, commonly used in computation as a
      factor, expressing the amount of some change or effect
      under certain fixed conditions as to temperature, length,
      volume, etc.; as, the coefficient of expansion; the
      coefficient of friction.
      [1913 Webster]

   Arbitrary coefficient (Math.), a literal coefficient placed
      arbitrarily in an algebraic expression, the value of the
      coefficient being afterwards determined by the conditions
      of the problem.
      [1913 Webster]