The story
From Charles Messier (1730-1817), the French astronomer who first published his Catalogue of Nebulae and Star Clusters in 1774.
Etymology from Wiktionary, CC BY-SA 4.0.
Messier number
Today it means: A catalogue number used to identify any one of more than one hundred galaxies, nebulae, and other deep-sky objects visible in the night sky; the designation formed by the surname Messier or letter M being prepended to the number, as in Messier 31 or M31 (the Andromeda Galaxy). Full definition →