A snort is a sound you make by suddenly exhaling through your nose, especially if you're disgusted by something. Your response to your little brother's tempter tantrum might be a disdainful snort.
You can use the word snort as a noun or a verb — students might find it hard not to snort when they're listening to a boring and endless lecture by their vice principal. You and your friends may also snort with contempt when you're watching a really bad movie. In the fourteenth century, to snort meant to snore — it wasn't until the 1800's that snort came to mean "verbally express contempt."