as hard as one can; to the best of one's ability

letter challenging someone to a duel

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

talking about oneself (especially, when the audience is not interested)

soul-searching

a photograph of oneself, a photographic self-portrait / (especially) a selfie

to take a photograph of oneself, to take a selfie

myself, oneself