Brewer's: Hip! Hip! Hurrah!
Hip is said to be a notarica, composed of the initial letters of Hicrosolyma Est Perdita. Henri van Laun says, in Notes and Queries, that whenever the German knights headed a Jew-hunt in the Middle Ages, they ran shouting “Hip! Hip!” as much as to say “Jerusalem is destroyed.” (See Notarica.)
Timbs derives Hurrah from the Sclavonic hu-raj (to Paradise), so that Hip! hip! hurrah! would mean “Jerusalem is lost to the infidel, and we are on the road to Paradise.” These etymons may be taken for what they are worth. The word hurrah! is a German exclamation also.
In fine he doth apply one speciall drift. Which was to get the pagan on the hip, And having caught him right, he doth him lift By nimble sleight, and in such wise doth trip, That down he threw him.
Sir J. Harington.