補角 is read as ほかく (hokaku) and means supplement.
ほかく
hokaku
ほじょ
spotting (in weight training)
ほきょう
reinforcement
ほせい
correction
ほきゅう
supply
ほけつ
filling a vacancy
ほそく
supplement
おぎなう
to supplement
ほせいよさん
revised budget
ほかん
complementation
おぎない
replenishment
ほしゅう
supplementary lessons
ほどう
guidance