Definition of "sanguine"

What, what, ye sanguine, shallow-hearted boys!

c. 1588–1593 (date written), William Shakespeare, “The Lamentable Tragedy of Titus Andronicus”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act IV, scene ii]

I'll be no longer guilty of this sin; this sanguine coward, thisbed-presser, this horse-back-breaker, this huge hill of flesh.

c. 1597 (date written), William Shakespeare, “The First Part of Henry the Fourth, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act II, scene iv]

Eleonore Lemindre, aged 34, tailoress, of a sanguine lymphatic temperament, having suffered great depression of spirits, experienced, in the course of 1820, symptoms of what is called disease of the heart.

1833, R. J. Bertin, translated by Charles W. Chauncy, Treatise on the Diseases of the Heart, and Great Vessels, Philadelphia: Carey, Lea & Blnachard, page 188

Mrs. Weston was exceedingly disappointed—much more disappointed, in fact, than her husband, though her dependence on seeing the young man had been so much more sober: but a sanguine temper, though for ever expecting more good than occurs, does not always pay for its hopes by any proportionate depression. It soon flies over the present failure, and begins to hope again.

1815 December (indicated as 1816), [Jane Austen], chapter XVIII, in Emma: […], volume I, London: […] [Charles Roworth and James Moyes] for John Murray, pages 306–307

It was clear that Dr. Gwynne was not very sanguine as to the effects of his journey to Barchester, and not over anxious to interfere with the bishop.

1857, Anthony Trollope, “The Master and Tutor of Lazarus”, in Barchester Towers. […], copyright edition, volume II, Leipzig: Bernhard Tauchnitz, published 1859, page 101

When the railway was opened on August 2, 1897, it was expected that Cruden Bay, on the Aberdeenshire coast, would develop into a popular holiday resort, but this sanguine forecast was never fully realised.

1949 May and June, “Notes and News: Closing of Boddam Branch”, in Railway Magazine, page 203

The plan was not feasible, for making a ninety-degree turn would have been impossible without nickel-alloy swivels inserted in the small of every man's back, and Lieutenant Scheisskopf was not sanguine at all about obtaining that many nickel-alloy swivels from Quartermaster or enlisting the cooperation of the surgeons at the hospital.

1961 November 10, Joseph Heller, “McWatt”, in Catch-22 […], New York, N.Y.: Simon and Schuster, page page

Maybe it was hormones, or the immersion of parenting a newborn, or a new appreciation for what my body could do, but I felt surprisingly sanguine about my wobbly physical state.

2022 February 2, Charlotte Cowles, “Can ‘Body Neutrality’ Change the Way You Work Out?”, in The New York Times