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 an arc or angle (Geom.), the difference between that arc or angle and 90░. -- Complement of a parallelogram. (Math.) See Gnomon. -- In her complement (Her.), said of the moon when represented as full.