Merriam-Webster Collegiate Dictionary - yaw

 I. noun  Etymology: origin unknown  Date: 1546  1. the action of ~ing; especially a side to side movement  2. the extent of the movement in ~ing  II. intransitive verb  Date: 1586  1.  a. of a ship to deviate erratically from a course (as when struck by a heavy sea); especially to move from side to side  b. of an airplane, spacecraft, or projectile to turn by angular motion about the vertical axis  2. alternate restlessly ~ing between apparent extremes — Martin Kasindorf