From The Collaborative International Dictionary of English v.0.48 [gcide]:
Yacht \Yacht\ (y[o^]t), n. [D. jagt, jacht; perhaps properly, a
chase, hunting, from. jagen to chase, hunt, akin to G. jagen,
OHG. jag[=o]n, of uncertain origin; or perhaps akin to OHG.
g[=a]hi quick, sudden (cf. Gay).] (Naut.)
A light and elegantly furnished vessel, used either for
private parties of pleasure, or as a vessel of state to
convey distinguished persons from one place to another; a
seagoing vessel used only for pleasure trips, racing, etc.
[1913 Webster]
Yacht measurement. See the Note under Tonnage, 4.
[1913 Webster]