Complement

The word complement (not to be confused with a different word, compliment) has a number of uses. Generally a complement of X is something that together with X makes a complete whole; that supplies what X lacks. The first e in complete and the first e in complement are etymological cognates of each other in a way that is a useful mnemonic for remembering that this is not compliment with an i.

• complementary color
• complement (biology) is a group of proteins of the complement system, found in blood serum which act in concert with antibodies to achieve the destruction of non-self particles such as foreign blood cells or bacteria.
• The article now titled complementary (which probably should be moved) deals with complementary experiments in physics and complementary strands of DNA or RNA molecules.
• complement (mathematics) (another disambiguation page)
• In traditional music theory a complement (music) is the interval added to another, that is placed on top of another, so that their complete span is an octave, while in musical set theory the complement of a pitch class set are those pitches not included (the pitches needed to form an aggregate).
• In optics, complement refers to complementary colors.
• In economics, a complement good is a good often consumed together with the good in question.
• phonetic complement