to answer one's own question

pupil (student) / studying under a teacher

specialist; expert

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

everything

(colloquial) current boyfriend

everyone, one and all

(slang) Alternative form of 彼氏 (kareshi, “boyfriend”)