"salty, briny," 1510s, from Dutch brak "brackish," probably from Middle Dutch brak "worthless," a word also used in commercial trade and which also made its way into early Modern English.
Entries linking to brack
brackish adj.
of water, "somewhat salty," 1530s, from Scottish brack "salty" (see brack) + -ish. Related: Brackishly; brackishness.