1530s, "abnormal" (usually in a bad sense), from Latin enormis "out of rule, irregular, shapeless; extraordinary, very large," from assimilated form of ex "out of" (see ex-) + norma "rule, norm" (see norm), with English -ous substituted for Latin -is. Meaning "extraordinary in size" is attested from 1540s; original sense of "outrageous" is more clearly preserved in enormity. Earlier was enormyous (mid-15c.) "exceedingly great, monstrous." Related: Enormously; enormousness.