means the size, extent, or importance of something — how big, how strong, or how significant it is.

from From Latin magnitudo, "greatness," built on magnus, "great" or "large" — the same root that swells through magnify, magnificent, and magnate. Magnus traces back to a Proto-Indo-European root meaning "great" (likely *meg-), a deep ancestor possibly related to Greek megas, as in megaphone. The word entered English in the late Middle Ages purely as a measure of greatness; only much later did science borrow it to grade earthquakes and the brightness of stars, where small numerical steps hide enormous leaps in scale.