tropic

Imagine a line wrapped around the Earth near the equator. That is the main idea of "tropic." In English, it usually means one of two special lines of latitude: the Tropic of Cancer in the north or the Tropic of Capricorn in the south. These lines mark the farthest points where the sun can appear directly overhead at noon during the year. They also help define the hot region of the world called the tropics. The word comes from Greek and carries the idea of the sun "turning" back after reaching these points.

The word "tropic" most often refers to either of two imaginary lines of latitude on Earth: the Tropic of Cancer, at about 23.5 degrees north, and the Tropic of Capricorn, at about 23.5 degrees south. These are not random map lines. They mark the most northern and most southern places where the sun can stand directly overhead at noon at some point in the year. The Tropic of Cancer has this position around the June solstice, and the Tropic of Capricorn around the December solstice.

Because of that, the word is closely tied to both geography and astronomy. The area between these two lines is known as the tropics, the part of the world generally associated with year-round warmth. In that sense, a tropic can also be understood as one of the boundary lines of that hot central zone of the Earth. The word comes from Greek and means "turning," pointing to the way the sun seems to change direction after reaching these limits.

In normal English, "tropic" is much less common by itself than in fixed names such as "the Tropic of Cancer" and "the Tropic of Capricorn." People more often use "tropics" for the region and "tropical" for the adjective. Still, if you understand "tropic" as a special line near the equator connected with the sun's yearly path, you have the heart of the word.