Terrible, a.
Etymology: [F., fr. L. terribilis, fr. terrere to frighten. See Terror.]
1. Adapted or likely to excite terror, awe, or dread; dreadful; formidable. Prudent in peace, and terrible in war. Prior. Thou shalt not be affrighted at them; for the Lord thy God is among you, a mighty God and terrible. Deut. vii. 21.
2. Excessive; extreme; severe. [Colloq.] The terrible coldness of the season. Clarendon.
Syn. -- Terrific; fearful; frightful; formidable; dreadful; horrible; shocking; awful. -- Ter"ri*ble*ness, n. -- Ter"ri*bly, adv.
Shades of meaning
Fernald has no entry of its own for terrible; he lists it under awful, formidable.
Where he writes about it:
Awful should not be used of things which are merely disagreeable or annoying, nor of all that are alarming and terrible, but only of such as bring a solemn awe upon the soul, as in the presence of a superior power; as, the awful hush before the battle. — from awful
Formidable is a word of more dignity than dangerous, and suggests more calm and collected power than terrible; formidable is less overwhelming than tremendous. — from formidable
A loaded gun is dangerous; a park of artillery is formidable; a charge of cavalry is terrible; the full shock of great armies is tremendous. — from formidable
A dangerous man is likely to do mischief, and needs watching; a formidable man may not be dangerous if not attacked; an enraged maniac is terrible; the force of ocean waves in a storm, and the silent pressure in the ocean depths, are tremendous. — from formidable