The Collaborative International Dictionary of English v.0.48:

Constat \Con"stat\, n. [L., it is evident.] (Law)
   A certificate showing what appears upon record touching a
   matter in question.
   [1913 Webster]

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

CONSTAT, English law. The name of a certificate, which the clerk of the pipe
and auditors of the exchequer make at the request of any person who intends
to plead or move in the court for the discharge of anything; and the effect
of it is, the certifying what constat (appears) upon record touching the
matter in question.
     2. A constat is held to be superior to an ordinary certificate, because
it contains nothing but what is on record. An exemplification under the
great seal, of the enrollment of any letters-patent, is called a constat. Co.

Litt. 225. Vide Exemplification; Inspeximus.
     3. Whenever an officer gives a certificate that such a thing appears of
record, it is called a constat; because the officer does not say that the
fact is so, but it appears to be as he certifies. A certificate that it
appears to the officer that a judgment has been entered, &c., is
insufficient. 1 Hayw. 410.