noun
temporary extra work; additional duty
Refers to work assigned on top of one's regular duties, often temporarily. Not a common everyday word; more likely to appear in workplace or bureaucratic contexts.
今月は加役が多くて、残業が増えた。
This month I have a lot of extra work, so my overtime has increased.
彼は加役を任されて、本来の業務に加えて報告書も書いている。
He was assigned additional duties and, on top of his regular work, is also writing reports.
Compound of 加 (add) and 役 (role, duty). The exact historical derivation is uncertain, but the meaning is transparent from its components.