Lewis & Short

mergae, ārum, f. [root marg-, to clear away; cf.: ἀμέργω, ἀμέλγω, mulgo, amurca], a two-pronged pitchfork, with which corn, when cut, was made into heaps: mergae furculae, quibus acervi frugum fiunt, dictae a volucribus mergis, quia, ut illi se in aquam mergunt, dum pisces persequuntur, sic messores eas in fruges demergunt, ut elevare possint manipulos, Paul. ex Fest, p. 124 Müll.: mergas datus, ut hortum fodiat, Plaut. Poen. 5, 2, 58: multi mergis, alii pectinibus spicam ipsam legunt, Col. 2, 21, 3.
Comically: si attigeris ostium, jam tibi hercle in ore fiet messio mergis pugneis, i. e. a rich crop of fisticuffs, Plaut. Rud. 3, 4, 58.