tropiko

The word is an astronomical instruction. A tropiko is strictly a line of latitude, and there are exactly two of them: the tropiko de Kancero in the north and the tropiko de Kaprikorno in the south. They are where the sun, having climbed higher in the sky each day, stops and turns back. Greek tropos is a turn, and the whole word means the turning one. Nobody standing in a hot country thinks about that, which is exactly why it is worth pointing out.

Two senses, one plural. In the strict sense, la tropiko is the line. In ordinary use, la tropikoj in the plural is the belt of the world between them, which is what English means by the tropics nine times in ten. Between them runs the equator, which Esperanto calls the ekvatoro, from Latin aequator, the equaliser, because day and night are equal there all year. That word has no page in this course yet.

The adjective does most of the work. Tropika means tropical: tropika klimato, tropika pluvo, tropika malsano. Subtropika is subtropical. Note that the geography words and the climate words are not the same set: klimato is the pattern of weather, ĝangalo is one kind of forest that grows in it, and varmega is what it feels like.