Meaning

noun a traveler who drives (or travels with) a dog team

originFrom mush (“to drive dogs, usually pulling a sled, across snow”) + -er (suffix forming agent nouns). Mush is probably derived from French marche or marchons, respectively the second-person singular and first-person plural imperative forms of marcher (“to move; to travel; to walk”), from Proto-Germanic *markōną (“to mark; to notice”), from *marką (“mark; sign; stamp”), possibly related to *markō…

Etymology from Wiktionary, CC BY-SA 3.0