In a manner that is unusual, irregular, or deviating from what is standard, expected, or normal.
From anomalous (Greek anomalos 'uneven' plus -ous, an adjectival suffix) combined with -ly, the standard adverbial marker. The term has been used in English since at least the 16th century to describe deviations from expected behavior or patterns.
When a scientist says something happened 'anomalously,' it's like they're waving a red flag saying 'this doesn't fit our model, and we need to figure out why!'
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