floater n. a person who files down or smooths horse teeth; a tool used for such a task. Etymological Note: Directly related to the verb “to float,” meaning “to file the teeth of a horse.” The Oxford English Dictionary includes a single 1886 citation supporting this specific sense of the verb, but the more general meaning, “to render smooth or level,” is dated to at least as early as 1703. Another specific sense, “to level (the surface of plaster) with a ‘float,’” does tentatively support a connection between the horse “float” and the plaster “float,” as mentioned in the 1982 citation. (source: Double-Tongued Dictionary)
Further reading
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Why is the rasp to file a horse’s teeth called a “float”?