A knitted jacket or jersey, usually of thick wool, worn by athletes before or after exercise.
"The track coach handed each runner a heavy wool sweater to keep warm during the cool mornings between races."
In plain English: A sweater is a warm, knitted shirt you wear to keep your body cozy when it's cold outside.
"She wore a cozy wool sweater to stay warm in the cold wind."
Usage: In everyday language, sweater refers to any loose-fitting garment with sleeves made of soft fabric like cotton or wool that covers the upper body and arms. While it can describe a specific athletic warm-up jacket in sports contexts, people most commonly use it for casual winter clothing worn over shirts.
To dress in a sweater.
"She decided to wear a warm wool sweater because the evening air turned chilly."
The word sweater comes from Middle English swētere, which was formed by combining the verb sweat with the suffix -er. Originally used to describe a person who sweats profusely, it eventually came into modern use for the garment designed to keep people warm.