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Webster 1828 Edition

adv.

With good or bad omens.

ominously ‎(comparative more ominously, superlative most ominously)

in an ominous manner; with sinister foreboding
- 1868, Wilkie Collins, The Moonstone‎
  From first to last he was ominously polite, and ominously silent.
- 1983, Patricia Hagan, Golden Roses
  His nostrils flared ominously and his fists opened and closed at his sides.

in an ominous manner