The Collaborative International Dictionary of English v.0.48:

Attentate \At*ten"tate\, Attentat \At*ten"tat\, n. [L.
   attentatum, pl. attentata, fr. attentare to attempt: cf. F.
   attentat criminal attempt. See Attempt.]
   1. An attempt; an assault. [Obs.] --Bacon.
      [1913 Webster]

   2. (Law)
      (a) A proceeding in a court of judicature, after an
          inhibition is decreed.
      (b) Any step wrongly innovated or attempted in a suit by
          an inferior judge.
          [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ATTENTAT, In the language of the civil and canon laws, is anything
whatsoever in the suit by the judge a quo, pending an appeal. 1 Addams, R.
22, n.; Ayl. Par. 100.