In a very obvious, shocking, or extremely noticeable way; to a great degree.
From 'gross' (from Latin 'grossus' meaning 'thick' or 'coarse') plus '-ly' to make an adverb. It originally described physical size but evolved to describe the degree or extent of something.
The word 'gross' once just meant physically thick or heavy, but now we use it to mean both disgusting AND to mean 'in total'—gross income, gross misjudgment—showing how one word can split into different meanings!
Complete word intelligence in one call. Free tier — 50 lookups/day.