magnitude (n.)
c. 1400, "greatness of size or character," from Latin magnitudo "greatness, bulk, size," from magnus "great" (from suffixed form of PIE root *meg- "great") + -tudo, suffix forming abstract nouns from adjectives and participles (see -tude). Meaning "size, extent" is from early 15c. Of stars, "brightness," from 1640s.