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Webster 1828 Edition

adv.

With alarm; in a manner to excite apprehension.

alarmingly ‎(comparative more alarmingly, superlative most alarmingly)

In an alarming way, frighteningly.
He sneezed alarmingly.
Causing fear or concern.
Alarmingly, he went into a severe sneezing fit.
To an extent that causes alarm.
He went into an alarmingly severe sneezing fit.

in an alarming manner, frighteningly. In a way the induces fear or concern