I. ˈkäm-plə-mənt noun
Etymology: Middle English, from Latin complementum, from complēre to fill up, complete, from com- + plēre to fill — more at full
Date: 14th century
1.
a. : something that fills up, completes, or makes perfect
b. : the quantity, number, or assortment required to make a thing complete
the usual complement of eyes and ears — Francis Parkman
especially : the whole force or personnel of a ship
c. : one of two mutually completing parts : counterpart
2.
a. : the angle or arc that when added to a given angle or arc equals a right angle in measure
b. : the set of all elements that do not belong to a given set and are contained in a particular mathematical set containing the given set
c. : a number that when added to another number of the same sign yields zero if the significant digit farthest to the left is discarded — used especially in assembly language programming
3. : the musical interval required with a given interval to complete the octave
4. : an added word or expression by which a predication is made complete (as president in “they elected him president” and beautiful in “he thought her beautiful”)
5. : the thermolabile group of proteins in normal blood serum and plasma that in combination with antibodies causes the destruction especially of particulate antigens (as bacteria and foreign blood corpuscles)
[
complement 2a: ACB right angle, ACD complement of DCB (and vice versa), AD complement of DB (and vice versa)
]
II. -ˌment verb
Date: 1602
intransitive verb
obsolete : to exchange formal courtesies
transitive verb
1. : to be complementary to
the illustrations complement the text
2. obsolete : compliment