Ricochet

Meaning - Spring back;spring away from an impact (as a verb) and a glancing rebound(as a noun).

The origin of this french word is unknown. This was used as military term in earlier times to express the rebound of a projectile that strikes on a hard surface.It is said that during 18th century, field artillery, which was not,before Napolean's time,relied upon the ricochet of round shot.The term "ricochet" is now only applied, in modern rifle shooting, to the graze of a bullet that has struck short.

I came across its use in below line from The New York times "Some Muslim supporters of Mr. Obama seem to ricochet between dejection and optimism."

References: http://encyclopedia.jrank.org