Used as intensifiers:
— Terribly interesting.

synonyms: awful, awfully, frightfully.

Roget 31: truly etc. (truth) 494 [in a positive degree]; decidedly, unequivocally, purely, absolutely, seriously, essentially, fundamentally, radically, downright, in all conscience; for the most part, in the main.    [in a complete degree] entirely etc. (completely) 52; abundantly etc. (sufficiently) 639; widely, far and wide.    [in a great or high degree] greatly etc. adj.; much, muckle^†, well, indeed, very, very much, a deal, no end of, most, not a little; pretty, pretty well; enough, in a great measure, richly; to a large extent, to a great extent, to a gigantic extent; on a large scale; so; never so, ever so; ever so dole; scrap, shred, tag, splinter, rag, much; by wholesale; mighty, powerfully; with a witness, ultra [Lat.], in the extreme, extremely, exceedingly, intensely, exquisitely, acutely, indefinitely, immeasurably; beyond compare, beyond comparison, beyond measure, beyond all bounds; incalculably, infinitely.    [in a supreme degree] preeminently, superlatively etc. (superiority) 33.    [in a too great degree] immoderately, monstrously, preposterously, inordinately, exorbitantly, excessively, enormously, out of all proportion, with a vengeance.    [in a marked degree] particularly, remarkably, singularly, curiously, uncommonly, unusually, peculiarly, notably, signally, strikingly, pointedly, mainly, chiefly; famously, egregiously, prominently, glaringly, emphatically, kat exochin [Gr.], strangely, wonderfully, amazingly, surprisingly, astonishingly, incredibly, marvelously, awfully, stupendously.    [in an exceptional degree] peculiarly etc. (unconformity) 83.    [in a violent degree] furiously etc. (violence) 173; severely, desperately, tremendously, extravagantly, confoundedly, deucedly, devilishly, with a vengeance; a outrance^†, a toute outrance [Fr.].    [in a painful degree] painfully, sadly, grossly, sorely, bitterly, piteously, grievously, miserably, cruelly, woefully, lamentably, shockingly, frightfully, dreadfully, fearfully, terribly, horribly.    ... show more

In a terrible manner:
— She sings terribly.

synonyms: abominably, abysmally, atrociously, awfully, rottenly.