Navigation is essentially an applied science and touches many other fields, borrowing copiously from their terminology. If terms relating primarily to such branches of science as astronomy, cartography, electronics, mathematics, meteorology, oceanography, surveying, etc., are found in these pages, it is because the navigator's sphere of interest overlaps these fields. An attempt has been made to define such terms in the language and from the viewpoint of the navigator. Only those meanings more or less directly related to navigation have been included.