Definition of "relent"

There was no relent, my dear, as we pulled each other in.

2015, Mel Parsons (lyrics and music), “First Sign of Trouble”

The pistons of this engine moved without relent.

2016, Colson Whitehead, The Underground Railroad, Fleet (2017), page 193

She forward went […] Ne rested till she came without relent Unto the land of Amazons.

1596, Edmund Spenser, “Book V, Canto VII”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie

Can you, my Lord of Winchester, beholdMy sighs and tears and will not once relent?

1591 (date written), William Shakespeare, “The First Part of Henry the Sixt”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene i]

Only the valley where Sish rested when he and Time were young did Sish not provoke his hours to assail. There he restrained his old hound Time […] For the minds of the gods relent towards their earliest memories, who relent not otherwise at all.

1905, [Edward Plunkett,] Lord Dunsany, The Gods of Pegāna‎, London: Elkin Mathews, […]

I did, I suppose, hope that she might finally relent a little and make some conciliatory response or other.

1989, Kazuo Ishiguro, The Remains of the Day

But nothing might relent her hastie flight; / So deepe the deadly feare of that foule swaine / Was earst impressed in her gentle spright […]

1590, Edmund Spenser, “Book III, Canto IV”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie

[Salt of tartar] placed in a cellar will […] begin to relent.

1669, Robert Boyle, The History of Fluidity and Firmness

When opening buds salute the welcome day, / And earth, relenting, feels the genial ray.

1717, Alexander Pope, “Eloisa to Abelard”, in The Works of Mr. Alexander Pope, volumes (please specify |volume=I or II), London: […] W[illiam] Bowyer, for Bernard Lintot, […], published 1717