Lewis Short
(verb) : com-prōmitto (conp-), mīsi, missum, 3 (contr. form conpromesise = conpromisisse, S. C. Bacch. v. 14), , jurid. t. t. in lawsuits
* To promise mutually to abide by the decision of an arbiter: tribunicii candidati conpromiserunt,Cic. Q. Fr. 2, 14 (15, 6): de aliquā re,Dig. 4, 8, 13: in arbitrum,ib. 44, 4, 4; 4, 8, 21 al.
* To promise at the same time (very rare): eisque spolia peremptorum hostium compromittens,Cassiod. Hist. Eccl. 6, 1.
Charlton T. Lewis, Charles Short, A Latin Dictionary