Wiktionary
noonday devil
n. Literally, a demon thought to be active at the noon hour which inclines its victims (usually monastics) to restlessness, excitability and inattention to one's duties. Used as a synonym for (term: acedia) (Gk. ''ακηδία'').
Usage examples of "noonday devil".
He remained seated by the water, listening to the song of the birds, who were celebrating morning, then the cicadas, at the hour when the noonday devil rages.