A complement is something that completes something else. Complement may refer specifically to: The arts Complement (music), an interval that, when added to another, spans an octave Aggregate complementation, the separation of pitch-class collections into complementary sets Complementary color, in the visual arts Biology and medicine Complement system (immunology), a cascade of proteins in the blood that form part of innate immunity Complementary DNA, DNA reverse transcribed from a mature mRNA template Complementarity (molecular biology), a property whereby double stranded nucleic acids pair with each other Complementation (genetics), a test to determine if independent recessive mutant phenotypes are caused by mutations in the same gene or in different genes Grammar and linguistics Complement (linguistics), a word or phrase having a particular syntactic role Subject complement, a word or phrase adding to a clause's subject after a linking verb Phonetic complement Complementary, a type of opposite in lexical semantics (sometimes called an antonym) Mathematics Algebra Complement (group theory) Complementary subspaces Orthogonal complement Schur complement Algorithms Complement (complexity), relating to decision problems and complexity classes Complement operator (regular expressions) Method of complements, in computer science Radix complement Diminished radix complement Ones' complement Two's complement Discrete mathematics Complement graph Self-complementary graph, a graph which is isomorphic to its complement Complemented lattice Geometry Complementary angles Knot complement Complement of a point, the dilation of a point in the centroid of a given triangle, with ratio −1/2 Logic Complement (set theory) Complementary event in probability Logical complement Bitwise complement Complements in boolean algebra Other uses Complementary experiments, in physics Complement good (economics), a good often consumed together with another good Ship's complement, the number of persons in a ship's company See also Complementarity (disambiguation) Compliment (disambiguation) Complimentary (disambiguation)