work done for free, unpaid work, uncompensated work / work done in vain, work with no favorable end result

to work for free, to work without pay or other compensation / to work in vain, to work with no favorable end result

(archaic, grammar) any word that declines or conjugates / (archaic, grammar) more specifically, a verb

someone else's younger sister

sworn younger sister

younger paternal half sister

a wife's sister

(archaic, men's speech) an intimate form of address for a female by a male: "my sister"

(formal) we, us

(honorific) we; us