The Collaborative International Dictionary of English v.0.48:

Essoin \Es*soin"\or Essoign \Es*soign\, n. [OF. essoine,
   essoigne, F. exoine, L. essonia, exonia; pref. ex- (L. ex
   from) + sunnis, sunnia, sonia, hindrance, excuse. Cf. Icel.
   syn refusal, synja to deny, refuse, Goth. sunja truth,
   sunj[=o]n to justify, OS. sunnea impediment, OHG. sunna.]
   1. (Eng. Law) An excuse for not appearing in court at the
      return of process; the allegation of an excuse to the
      court.
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   2. Excuse; exemption. [Obs.]
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            From every work he challenged essoin. --Spenser.
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   Essoin day (Eng. Law), the first general return day of the
      term, on which the court sits to receive essoins.
      --Blackstone.
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