thun·der·ing I. \ˈthənd(ə)riŋ, -rēŋ\noun (-s) Etymology: Middle English thondring, from Old English thunring, from thunrian to thunder + -ing : thunder II. adjective Etymology: from present participle of thunder (II) : awesome in virtue of impressive greatness, magnitude, or unusualness < the thundering silence of what was left unsaid — A.E.Stevenson b.1900 > < a thundering success as a salesman — R.H.Rovere > • thun·der·ing·lyadverb