English▸ adjective deviating from what is normal or usual, typically in a way that is undesirable or worrying:
the illness is recognizable from the patient's abnormal behavior
participants with abnormal results were invited to undergo further diagnostic testing.
– ORIGIN mid 19th century : alteration (by association with Latin abnormis ‘monstrous’) of 16th-century anormal, from French, variant of anomal, via Latin from Greek anōmalos (see anomalous).