But the truth is,—and why should I not confess it?—I am not plethorically abounding in cash at this present. Merit, Heaven knows, is very little rewarded; but it does not become me to speak of myself. My motto is, 'contented with little, yet wishing for more.'

According to the Oxford English Dictionary, this is the earliest occurrence of the word in print. The date of the letter is supplied by the OED, based on a 1976 source.