I just came across a question on skeptics.SE that asked whether it is possible to sail a boat from the coast of Pakistan to the east coast of Russia in an uninterrupted straight line. A quick glance at a globe suggests that there's nothing to be really skeptical about (the OP may have been misled by the planar nature of map projections). But while thinking about the question, I realized that I don't know the right terminology to describe the changes to the bearing on board of the ship.
As a rough estimate, a ship sailing from Karachi to the Kamchatka Peninsula will start with a bearing of perhaps 210° (relative to true north). If it continues its course in a straight line, it will be sailing basically parallel to the meridians with a bearing of 270° roughly by the time the ship has reached the South Sandwich Islands. The bearing at the Equator will be somewhere in the vicinity of 330°, and it will arrive at Kamchatka with a bearing of about 290°.
What is the right term to refer to this phenomenon that the true bearing changes if you move in a straight line in a non-cardinal direction on a globe? I keep thinking of "declination", but this is probably because I'm aware of what magnetic declination is.