Definition from Wiktionary, the free dictionary
Audio (US) (file)
- (literary or dated) Causing terror or awe.
- The lion roared terribly.
- Very; extremely.
- He's terribly busy and you really shouldn't bother him.
- 2011 December 15, Felicity Cloake, “How to cook the perfect nut roast”, Guardian:
- The parsnip, stilton and chestnut combination may taste good, but it's not terribly decorative. In fact, dull's the word, a lingering adjectival ghost of nut roasts past that I'm keen to banish from the table. Mary Berry wraps her version in strips of chargrilled aubergine but, although it looks rather smart, I worry that something so Mediterranean will stick out like a sore thumb on the plate, given that many vegetarians want to enjoy the same roast potatoes, sprouts and sauces as everyone else. Instead, inspired by the stuffed cabbage rolls eaten at Christmas in the Balkans and Eastern Europe, I use blanched savoy cabbage leaves to wrap my parsnippy parcel, adding a touch of festive greenery to the dish.
- Very badly.
- She even signed up for karaoke, although she sang terribly.
Usage notes 
- Adjectives to which "terribly" is often applied: wrong, sorry, important, difficult, hard, afraid, sad, bad, expensive, long, upset, exciting, fast, excited, slow, cold, hot, busy, concerned, pleased, interesting, painful, funny, lonely, ill, good, tired, strong, confused, serious, fond, old, angry, anxious, effective, depressed, familiar, attractive, happy, poor, hungry, sick, big, nice, small, dull, clever, dirty, proud, disappointing, sweet, original, ashamed, efficient, successful, jealous, simple, strange, cruel.
in a terrible manner