n. [ LL. deviatio: cf. F. déviation. ] 1. The act of deviating; a wandering from the way; variation from the common way, from an established rule, etc.; departure, as from the right course or the path of duty. [ 1913 Webster ]

2. The state or result of having deviated; a transgression; an act of sin; an error; an offense. [ 1913 Webster ]

3. (Com.) The voluntary and unnecessary departure of a ship from, or delay in, the regular and usual course of the specific voyage insured, thus releasing the underwriters from their responsibility. [ 1913 Webster ]

4. (Statistics, Physics) the difference between an expected value of an observation or measurement and the actual value. [ PJC ]

Deviation of a falling body (Physics), that deviation from a strictly vertical line of descent which occurs in a body falling freely, in consequence of the rotation of the earth. --
Deviation of the compass, the angle which the needle of a ship's compass makes with the magnetic meridian by reason of the magnetism of the iron parts of the ship. --
Deviation of the line of the vertical, the difference between the actual direction of a plumb line and the direction it would have if the earth were a perfect ellipsoid and homogeneous, -- caused by the attraction of a mountain, or irregularities in the earth's density. [ 1913 Webster ]