GNU Collaborative International Dictionary of English

Found one definition

1.       
   Æ or Ae. A diphthong in the Latin language; used also by the Saxon writers. It corresponds to the Gr. αι. The Anglo-Saxon short æ was generally replaced by a, the long ǣ by e or ee. In derivatives from Latin words with ae, it is mostly superseded by e. For most words found with this initial combination, the reader will therefore search under the letter E.
   1913 Webster