Definition of "unrequited"

Enough for me that I stand on the privilege of a free Scottish-man, and will brook no insult unreturned, and no injury unrequited.

1820 March, [Walter Scott], chapter VI, in The Monastery. A Romance. […], volume II, Edinburgh: […] Longman, Hurst, Rees, Orme, and Brown, […]; and for Archibald Constable and Co., and John Ballantyne, […], page 196

One of my comrades there—another of those victims of eighteen years of unrequited toil and blighted hopes—was one of the gentlest spirits that ever bore its patient cross in a weary exile: [...]

1870–1871 (date written), Mark Twain [pseudonym; Samuel Langhorne Clemens], chapter LXI, in Roughing It, Hartford, Conn.: American Publishing Company [et al.], published 1872, page 439

To her mind, a girl who would tell of the unrequited love of a man for herself, was unspeakably base.

1912, Eleanor H. Porter, chapter 27, in Miss Billy’s Decision