General English

  • noun a thing which adds to or fits in with something else
  • noun a noun or adjective which follows the verbs ‘be’ or ‘become’


  • verb to fit in with and improve the performance of something



  • One good is a complement for another if an increase in demand for one (or a fall in its price) causes an increase in the demand for the other. Opposite of substitute.


  • The numerical result obtained when a number is subtracted from the radix, which is the number of digits used in a numbering system. For instance, the complement of 6 in the decimal number system is 4: (10 -6) = 4. The complement of a number in the binary number system is the other. 1 is the complement of 0, and 0 is the complement of 1. Used in computers, for instance, to represent negative numbers. Also called true complement, or radix complement.

Health Economics

  • (written as Complement)
    A good or service whose demand rises or falls as the price of another good falls or rises is said to be a complement. The cross-elasticity of demand is negative. Infliximab and methodextrate, two drugs used in combination in the treatment of rheumatoid arthritis, are an example. So are golf clubs and balls. They tend to be goods that are used together.


  • noun a substance which forms part of blood plasma and is essential to the work of antibodies and antigens
  • verb to complete something by providing useful or pleasing qualities which it does not itself have