Synonyms of threateningly

2 Syllables
quite, very, badly
3 Syllables
sorely, gravely, grievously, malignly, fiercely, harmfully
4 Syllables
distressingly, intensely, severely, regrettably, deplorably, acutely, frighteningly, tigerishly, menacingly, perilously, precariously, decidedly
5 Syllables
maleficiently