Complement Com"ple*ment, n. [L. complementun: cf. F. compl['e]ment. See Complete, v. t., and cf. Compliment.] 1. That which fills up or completes; the quantity or number required to fill a thing or make it complete. 2. That which is required to supply a deficiency, or to complete a symmetrical whole. History is the complement of poetry. --Sir J. Stephen. 3. Full quantity, number, or amount; a complete set; completeness. To exceed his complement and number appointed him which was one hundred and twenty persons. --Hakluyt. 4. (Math.) A second quantity added to a given quantity to make it equal to a third given quantity. 5. Something added for ornamentation; an accessory. [Obs.] Without vain art or curious complements. --Spenser. 6. (Naut.) The whole working force of a vessel. 7. (Mus.) The interval wanting to complete the octave; -- the fourth is the complement of the fifth, the sixth of the third. 8. A compliment. [Obs.] --Shak. Arithmetical compliment of a logarithm. See under Logarithm. Arithmetical complement of a number (Math.), the difference between that number and the next higher power of 10; as, 4 is the complement of 6, and 16 of 84. Complement of anarc or angle (Geom.), the difference between that arc or angle and 90[deg]. Complement of a parallelogram. (Math.) See Gnomon. In her complement (Her.), said of the moon when represented as full.