or Bosporus, in geography, a long and narrow sea, which it is supposed a bullock may swim over. In a more general sense, it is a long narrow sea running in between two lands, or separating two continents, and by which two seas, or gulfs and a sea, are made to communicate with each other: In which sense, bosporus amounts to the same with what we otherwise call an arm of the sea, channel, or strait; the Italians, fario; the Latins, fretum; and the French, pas, manche. The word is Greek, βόσφορος, formed from βός "bullock," and φόρος "passage."

The name bosphorus, is chiefly confined to two straits in the Mediterranean sea, viz. the bosphorus of Thrace, commonly called the straits of Constantinople, or channel of the Black Sea; and the Cimmerian or Scythian bosphorus, so called, it seems, from its resemblance to the Thracian; now more commonly the straits of Kapoia, or Kiderleri, from two cities standing on it.

The origin of the name is better agreed on than the reason why it was first given to the Thracian bosphorus. Nymphius tells us, on the authority of Accarion, that the Phrygians, desiring to pass the Thracian strait, built a vessel, on whose prow was the figure of a bullock; and which was hence called βός, "bullock;" and served them for a ferry-boat. Dionysius, Valerius Flaccus, Callimachus, Apollodorus, Marcellinus, &c., say, that it, being transformed into a cow by Juno, passed this strait swimming, which hence was called bosphorus. Arrian tells us, that the Phrygians were enjoined by the oracle, to follow the rout which a bullock should mark out to them; and that, upon stirring one up, it jumped into the sea to avoid their pursuit, and swam over this strait. Others say, that an ox, tormented by a gad-fly, threw itself in, and swam over; and others, that anciently the inhabitants of these coasts, when they would pass over, joined little boats together, and had them drawn over by bullocks, &c.