Definition of "soporific"

And ancient soporifics—such as poisonous leaves and various opiate concoctions—were roughly as likely to kill you as they were to induce REM.

2022 January 27, Derek Thompson, “Can Medieval Sleeping Habits Fix America’s Insomnia?”, in The Atlantic‎

For we are not here to understand, as perhaps some have, that an author actually falls asleep while he is writing. It is true, that readers are too apt to be so overtaken; […] To say the truth, these soporific parts are so many scenes of serious artfully interwoven, in order to contrast and set off the rest;

1749, Henry Fielding, chapter I, in The History of Tom Jones, a Foundling, volumes (please specify |volume=I to VI), London: A[ndrew] Millar, […], book V

It is said that the effect of eating too much lettuce is “soporific.” I have never felt sleepy after eating lettuces; but then I am not a rabbit. They certainly had a very soporific effect upon the Flopsy Bunnies!

1909, Beatrix Potter, The Tale of The Flopsy Bunnies

I should imagine that the smooth riding and the quietness of the diesel or electric cab, coupled with the effect on the eyes of endless successions of sleepers disappearing from sight immediately under the driver's eyes, might in time have a soporific effect, so that the company of a second man, who can assist in signal observations when he is not at work in the engine cab, seems highly desirable in such conditions.

1961 July, Cecil J. Allen, “Locomotive Running Past and Present”, in Trains Illustrated, page 401

COP stands for conference of the parties under the UNFCCC, and the annual meetings have swung between fractious and soporific, interspersed with moments of high drama and the occasional triumph (the Paris agreement in 2015) and disaster (Copenhagen in 2009).

2019 December 2, Fiona Harvey, “Climate crisis: what is COP and can it save the world?”, in The Guardian‎