Other forms: bullhorns
A bullhorn is a hand-held device that makes your voice sound much louder when you speak into it. You might address a crowd at a rally or protest by talking into a bullhorn.
While in the US, most people know what a bullhorn is, in other places it's called a megaphone. Bullhorns amplify sound, sometimes simply using their cone-like shape, and in other cases using electricity. Anyone who needs to get the attention of a large or noisy group might use a bullhorn to be heard. The word may be based on the shape of a bull's horn, although experts aren't sure about its origin.