abnormal (adj.)
1835, displaced older abnormous (1742) and rival anormal (1835) under influence of Latin abnormis "deviating from a rule," from ab- "off, away from" (see ab-) + norma "rule" (see norm). The older forms were via Old French anormal (13c.), from Medieval Latin anormalos, from Greek anomalos, from an- "not" + homalos, from homos "same." The Greek word was altered in Latin by association with norma. Related: Abnormally.