Abnormally means in a way that departs worryingly from the usual. Abnormally high, abnormally quiet, behaving abnormally.
It carries alarm where unusually does not, which is why medical and weather reports use it deliberately. It is a statement about a range rather than about right and wrong.
1adverbabnormallyIn a way that departs worryingly from the usual.
“The weather has been abnormally warm for December.”
abnormally is a manner.
Ancient Greek
ἀνώμαλος
Latin
abnormis — departing from normal
English
abnormal
English, today
abnormally
From abnormal + -ly. abnormal comes from ab- + normal. From ab- + normal. First attested in 1835, replacing the earlier anormal and even earlier abnormous, from Latin abnormis (“departing from normal”), from either ab- + norma, or Ancient Greek ἀνώμαλος.
Etymology from Wiktionary, CC BY-SA