Commonly means in most cases, and by most people. Commonly used, commonly known as, commonly believed.
Commonly known as is the standard way of giving a plain name beside a technical one. It reports frequency and not correctness, so commonly believed is often the polite opening of a correction.
1adverbcommonlyIn most cases, and by most people.
“Paracetamol is commonly used to treat headaches and fevers.”
commonly is a frequency.
Common plus -ly, from Latin communis, shared by all.
Middle English
comunly
English, today
commonly
Middle English comunly; equivalent to common + -ly.
Etymology from Wiktionary, CC BY-SA