Definition of "imbitter"

The superstition of the people was not imbittered by any mixture of theological rancor; nor was it confined by the chains of any speculative system.

1776, Edward Gibbon, chapter II, in The History of the Decline and Fall of the Roman Empire, volume I, London: […] W[illiam] Strahan; and T[homas] Cadell, […]

Their pleasures, poor as they were, could not be preserved pure, but were imbittered by petty competitions, and worthless emulation.

1825, Samuel Johnson, Dr. Johnson's Works: Life, Poems, and Tales, Volume 1‎

It is with extreme reluctance that I dwell upon the appalling scene which ensued; a scene which, with its minutest details, no after events have been able to efface in the slightest degree from my memory, and whose stern recollection will imbitter every future moment of my existence.

1838, [Edgar Allan Poe], chapter XII, in The Narrative of Arthur Gordon Pym of Nantucket. […], New York, N.Y.: Harper & Brothers, […], page 107

But my joy on reaching the east coast was sadly imbittered by the news that Commander MacLune […] had, with Lieutenant Woodruffe and five men, been lost on the bar.

1873, David Livingstone, Missionary Travels and Researches in South Africa‎

Naturally the Tennesseeans, conscious that they had not wronged the Indians, and had scrupulously observed the treaty, grew imbittered over, the wanton Indian outrages.

1889, Theodore Roosevelt, The Winning of the West, Volume Four‎