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Etymology and meanings

First attested in English in the early 14th century, the word "navy" came via Old French navie, "fleet of ships", from the Latin navigium, "a vessel, a ship, bark, boat", from navis, "ship". The word "naval" came from Latin navalis, "pertaining to ship"; cf. Greek ναῦς (naus), "ship", ναύτης (nautes), "seaman, sailor". The earliest attested form of the word is in the Mycenaean Greek compound word 𐀙𐀄𐀈𐀗, na-u -do-mo (* naudomoi), "shipbuilders", written in Linear B syllabic script.

The word formerly denoted fleets of both commercial and military nature. In modern usage "navy" used alone always denotes a military fleet, although the term " merchant navy " for a commercial fleet still incorporates the non-military word sense. This overlap in word senses between commercial and military fleets grew out of the inherently dual-use nature of fleets; centuries ago, nationality was a trait that unified a fleet across both civilian and military uses. Although nationality of commercial vessels has little importance in peacetime trade other than for tax avoidance, it can have greater meaning during wartime, when supply chains become matters of patriotic attack and defense, and when in some cases private vessels are even temporarily converted to military vessels. The latter was especially important, and common, before 20th-century military technology existed, when merely adding artillery and naval infantry to any sailing vessel could render it fully as martial as any military-owned vessel. Such privateering has been rendered obsolete in blue-water strategy since modern missile and aircraft systems grew to leapfrog over artillery and infantry in many respects; but privateering nevertheless remains potentially relevant in littoral warfare of a limited and asymmetric nature.