Source : Webster's Revised Unabridged Dictionary (1913)

Birr \Birr\, v. i. [imp. & p. p. {Birred}; p. pr. & vb. n.
   {Birring}.] [Cf. OE. bur, bir, wind, storm wind, fr. Icel.
   byrr wind. Perh. imitative.]
   To make, or move with, a whirring noise, as of wheels in
   motion.

Birr \Birr\, n.
   1. A whirring sound, as of a spinning wheel.

   2. A rush or impetus; force.

Source : WordNet®

birr
     n 1: the basic unit of money in Ethiopia; equal to 100 cents
     2: sound of something in rapid motion; "whir of a bird's
        wings"; "the whir of the propellers" [syn: {whir}, {whirr},
         {whirring}]
     v : make a soft swishing sound; "the motor whirred"; "the car
         engine purred" [syn: {whizz}, {whiz}, {whirr}, {whir}, {purr}]