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Webster 1913 Edition

adv.

In a strange, unearthly way.

eerily ‎(comparative more eerily, superlative most eerily)

In an eerie manner.
- 2006 September 11, Sheryl Gay Stolberg, “Bush Mourns 9/11 at Ground Zero as N.Y. Remembers”, in New York Times:
  A woman whose fiancé died on Sept. 11, Maria Barreto-Mojica, said she noticed that something about yesterday had seemed eerily familiar. “I looked at the sky this morning. It was so blue, just the same as it was that morning,” said Ms. Barreto-Mojica, 48, who was to marry fire lieutenant Dennis Mojica.

In an eerie manner