The story
18th century, in the sense "magnitude (brightness class) of a star", informed by the Greek τῶν μεγάλων τάξις (tôn megálōn táxis) (Ptolemy).
Etymology from Wiktionary, CC BY-SA 4.0.
order of magnitude
Today it means: The class of scale or magnitude of any amount, where each class contains values of a fixed ratio (most often 10) to the class preceding it. Full definition →