tropical

Pluraltropicals

1. 1
   adjective

   Belonging to or characteristic of the tropics, the warm region of Earth lying between about 23 degrees north and 23 degrees south of the equator.

   Many tropical nations lie within a few degrees of the equator.

   The expedition studied rainfall patterns across the tropical belt.

   Similarequatorial

   Oppositepolar

   Note

   Built from tropic plus -al, the word first points to a place on the map: the band between the Tropic of Cancer and the Tropic of Capricorn, where the sun can stand directly overhead. Used this way it is a matter of latitude, not weather. A tropical nation is one inside those lines. The "hot and humid" meaning grew from the climate those latitudes are known for.

2. 2
   adjective

   Coming from a hot, humid climate, or having the warm, moist quality of one.

   The bathroom turned tropical after his long, steaming shower.

   By midday the swamp air had grown tropical and heavy.

   Similarhumid, steamy, sultry, muggy, sweltering

   Oppositecold, chilly, frigid, arctic

   Note

   Here the word describes conditions rather than coordinates, so it travels: a summer far from the equator can still bring tropical nights. It pairs readily with fruits, waters and species. Richard Ellis's The Book of Sharks (1983) shows the contrast it carries: whale sharks keep to tropical waters, though an occasional stray wanders into colder ones.

3. 3
   nouncountable

   A plant that grows in or comes from the warm, humid tropics.

   The nursery's back room was crowded with tropicals from the rainforest.

   A tropical like this won't survive a hard frost.

   Note

   The adjective turned into a gardener's noun, with the regular plural tropicals. It treats a plant's origin as a category of its own. The Horticulturist of 1856 calls the potato a mountain tropical plant, hardier in cool weather than "any other tropical." That is the noun's typical work: sorting plants by how much warmth they need.

4. 4
   adjective

   Relating to tropical geometry, a branch of mathematics built on a number system where addition is replaced by taking the minimum or maximum and multiplication by ordinary addition.

   The seminar explored how tropical curves arise from polynomial equations.

   Researchers used a tropical approach to simplify the optimization problem.

   Note

   Nothing here is warm: the word labels a whole arithmetic and everything built on it. Mathematicians speak of tropical addition, tropical polynomials and the tropical semiring. Under those rules, polynomial equations describe shapes made of straight pieces, so a tropical curve looks like a network of line segments. Whether the convention uses the minimum or the maximum, the adjective stays the same.

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