Æ

from The Century Dictionary.

• One.
• The nominative plural termination of Latin and Latinized Greek words in -a (in Latinized Greek also -e, -as, -es) of the first declension, feminine, sometimes masculine.
• A character in the Anglo-Saxon alphabet representing a simple vowel, having when short the sound of English a in glad (ă), and when long the sound of English a in glare, dare, etc. (ã), as commonly pronounced in the United States.
• A digraph or ligature appearing in Latin and Latinized Greek words.
• The symbol used in Lloyd's Register for third-class wooden and composite ships.

from the GNU version of the Collaborative International Dictionary of English.

• A diphthong in the Latin language; used also by the Saxon writers. It answers to the Gr. ai. 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 In derivatives from Latin words with ae, it is mostly superseded by e. For most words found with this initial combination, the reader will therefore search under the letter E.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A ligature from the letters A and E.
• noun Ligature of vowels A and E.
• proper noun The pseudonym of the Irish writer George William Russell.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun Irish writer whose pen name was A.E. (1867-1935)