The Collaborative International Dictionary of English v.0.48:

Yester \Yes"ter\, a. [See Yesterday.]
   Last; last past; next before; of or pertaining to yesterday.
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         [An enemy] whom yester sun beheld
         Mustering her charms.                    --Dryden.
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   Note: This word is now seldom used except in a few compounds;
         as, yesterday, yesternight, etc.
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