supplementary
adjective uk/ˌsʌp.lɪˈmen.tər.i/ us/ˌsʌp.ləˈmen.t̬ɚ.i/
(ANGLE)
mathematics specialized（角）互补的
If an angle is supplementary to another angle, it forms 180° when combined with it.
(EXTRA)
C2 mainly UK (US usually supplemental)额外
extra
a supplementary income 额外收入