1. Either of the two parallels of latitude 23°27′north and south of the equator; the farthest points at which the sun can be directly overhead; the boundaries of the torrid zone or tropics.


  1. Of, or relating to the tropics; tropical.
  2. hot and humid.
  3. (noncomparative) Having the quality of indirectly inducing a biological or chemical change in a system or substrate.
    The binding of oxygen to hemoglobin is allosterically regulated by various tropic factors, such as BPG and acidity.

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