To shiver means to shake slightly and uncontrollably, usually because you're cold or frightened. When you step outside on a freezing winter morning without a jacket, your body starts to shiver: your muscles make quick, small movements trying to warm you up. You might shiver while waiting for the school bus in January, or shiver after jumping into a cold swimming pool.

Fear can also make you shiver. When you hear a spooky noise in a dark room, you might feel a shiver run down your spine (a single quick tremor of fear). Reading a ghost story might send shivers through you, even though you're perfectly warm.

The word works as both a verb (“I shivered in the cold”) and a noun (“A shiver passed through the audience”). When something gives you the shivers, it makes you feel uneasy or creeped out.

Your body shivers to generate heat through muscle movement. It's an automatic response you can't really control, which is why you might shiver even when you're trying hard to stay still. Animals shiver too: a wet dog will shiver after a bath, and birds fluff their feathers and shiver to stay warm in winter.