adjective /ˈtɛ.ɹə.bl̩/ˈtɛ.ɹɪ.bl̩/
The witch gave him a terrible curse.
b) Most formidable.
...and there was even a party of the younger men who pretended to admire him, calling him a "true sea-dog," and "real old salt," and such-like names, and saying there was the sort of man that made England terrible at sea.
Wikipedia foundation.