Lewis Short
pĭāmentum (noun N) : id.
* A means of expiation, an atoning sacrifice (perh. not anteAug.): terrae,Plin. 25, 9, 59, § 107; 25, 4, 11, § 30; cf.: piamenta, quibus utitur (in) expiando, Fest. s. v. piatrix, p. 213 Müll.; p. 238 ib.
* Trop., Sen. Cons. ad Helv. 16; Plin. 37, 1, 2, § 3.
Charlton T. Lewis, Charles Short, A Latin Dictionary