IPA: /ˈtɛrəbli/
KK: /ˈtɛrəbli/
In a way that is very bad or unpleasant; to a great extent.
She was terribly upset about the news.
Terribly → It is formed from "terrible" (from Latin *terribilis*, meaning causing terror or fear) and the suffix "-ly" (meaning in a manner of). The word "terribly" means in a manner that causes terror or fear, or to a great degree.
Think of something that causes 'terror' ('terrible') and remember that 'terribly' means in a way that is very intense or severe.