Firth of Forth an inlet of the North Sea in SE Scotland: spanned by a cantilever railway bridge 1600 m (almost exactly 1 mile) long (1889), and by a road bridge (1964)
2.
a river in S Scotland, flowing generally east to the Firth of Forth. Length: about 104 km (65 miles)
O.E. forðian "forward, onward," perf. of for(e), from P.Gmc. *furtha- (cf. O.N. forð, Du. voort, Ger. fort), from PIE *prto-, from the root of fore (q.v.).