SCARILY
frighteningly, scarily
(adverb) in an alarming manner; “the disturbing thing about the Minister’s behavior is that far from being artificial, it too often rings frighteningly true”
Source: WordNet® 3.1
Etymology
Adverb
scarily (comparative more scarily, superlative most scarily)
In a scary manner.
Source: Wiktionary
SCARY
Sca"ry, n. Etym: [Prov. E. scare scraggy.]
Definition: Barren land having only a thin coat of grass. [Prov. Eng.]
Scar"y, a. Etym: [From Scare.]
1. Subject to sudden alarm. [Colloq.U.S.] Whittier.
2. Causing fright; alarming. [Colloq.U.S.]
Source: Webster’s Unabridged Dictionary 1913 Edition