Lewis Short
(verb) : merto, 1, mergo, a collat. form of merso
* To immerse, overwhelm (anteclass.): mertat pro mersat dicebant, Paul. ex Fest. p. 124 Müll.; cf. Quint. 1, 4, 14: quos hic non mertet metus, Att. ap. Non. 138, 33; 138, 2.
Charlton T. Lewis, Charles Short, A Latin Dictionary