\Main"prise\, n. [F. main hand + prise a taking, fr.
prendre, p. p. pris to take, fr. L. prehendere, prehensum.]
(Law)
(a) A writ directed to the sheriff, commanding him to take
    sureties, called mainpernors, for the prisoner's
    appearance, and to let him go at large. This writ is now
    obsolete. --Wharton.
(b) Deliverance of a prisoner on security for his appearance
    at a day.

\Main"prise\, v. t. [imp. & p. p. {Mainprised}; p. pr.
& vb. n. {Mainprising}.] (Law)
To suffer to go at large, on his finding sureties, or
mainpernors, for his appearance at a day; -- said of a
prisoner.