complement
1. com.ple.ment \'ka:m-pl*-m*nt\ n [ME, fr. L complementum, fr. comple-re]
1a: something that fills up, completes, or makes perfect 1b: the quantity
or number required to make a thing complete; specif : the whole force or
personnel of a ship 1c: one of two mutally completing parts : COUNTERPART
2: the amount of angle or arc by which a given angle or arc falls short of
90 degrees 3: the interval in music required with a given interval to
complete the oct ave 4: an added word or expression by which a predication
is made complete (as president in "they elected him president") 5: the
thermolabile substance in normal blood serum and plasma that in comb
ination with antibodies causes the destruction of bacteria, foreign blood
corpuscles, and other antigens
2. com.ple.ment \-.ment\ vt 1: to be complementary to obs 2: COMPLIMENT
obs : to exchange formal courtesies