The Collaborative International Dictionary of English v.0.48:

Utas \U"tas\, n. [OF. huitieves, witieves, witaves, oitieves,
   pl. of huitieve, witieve, etc., eighth, L. octavus. See
   Octave, n.] [Written also utis.]
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   1. (O. Eng. Law) The eighth day after any term or feast; the
      octave; as, the utas of St. Michael. --Cowell.
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            The marriage was celebrated and Canterbury, and in
            the utas of St. Hilary next ensuing she was crowned.
                                                  --Holinshed.
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   2. Hence, festivity; merriment. [Obs.] --Shak.
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