a. [f. as TROPIC a.1 + -AL. Cf. mod.F. tropical.]
1. Astr. Pertaining or relating to the tropics, or either tropic (in sense A. 1 a or b). Chiefly in tropical year, the interval between two successive passages of the sun through the same ‘tropic’ or solstitial point (or, equivalently, through the same equinoctial point); the natural year of the seasons, as reckoned from one (winter or summer) solstice or (vernal or autumnal) equinox to the next. So tropical month, the time taken by the moon in passing from either tropic (or either equinoctial point) to the same again.
1527. R. Thorne, in Hakluyt, Voy. (1589), 252. The quantitie of the earth vnder the Equinoctiall to both the Tropicall lines.
1594. Blundevil, Exerc., III. I. xxxviii. (1636), 353. The Astronomicall yeere is either Tropicall or Syderall.
1662. Stanley, Hist. Chaldaic Philos. (1701), 17/2. Tropical [signs] are those to which when the Sun cometh he turneth back.
1715. trans. Gregory’s Astron. (1726), I. 408. The Tropical Year is that space of time wherein the same Seasons of the Year return again.
1812. Woodhouse, Astron., xxxi. 305. The tropical revolution of the Moon, or the revolution with respect to the equinoxes.
1834. Nat. Philos., III. Astron., i. 41/1 (Usef. Knowl. Soc.). The year from equinox to equinox is called the equinoctial year, or sometimes the tropical year.
1868. Lockyer, Elem. Astron., v. (1879), 203. The tropical month is the revolution of the moon with respect to the moveable equinox.
2. Geog. Pertaining to, occurring in, or inhabiting the tropics; belonging to the torrid zone.
1698. Froger, Voy., 3. At three o’clock in the morning we passed the tropick of Cancer;… and in the afternoon performed the ceremonies of Tropical baptism or duckings, which are commonly us’d by mariners in those places.
1699. Dampier, Voy., II. I. ii. 33. Many reasons … beside the accidental ones from the make of the particular Countries, Tropical Winds, or the like.
1747. T. Salmon, Modern Gazetteer, s.v. Tonquin. They have plenty of oranges, limes, coca nuts, pine-apples, plantains, mangoes, and other tropical fruits.
1788. Gibbon, Decl. & F., l. (1846), V. 2. The face of the desert … is scorched by the direct and intense rays of a tropical sun.
1851. Carpenter, Man. Phys. (ed. 2), 67. The highest temperature which the soil usually possesses in tropical climates, is about 126°.
1862. Dana, Man. Geol., 615. Coral formations are most abundant in the tropical Pacific.
1880. Haughton, Phys. Geog., vi. 272. The second and third of the sub-orders are confined to the tropical forests of South America.
b. Path. Applied to diseases to which one is liable in tropical regions.
1815. Morning Chron., 2 Sept., 2/3. The expedition arrived with 2000 sick, to the most unhealthy part of Venezuela, and their disorders were increased by tropical fevers, so that nearly all the sick have perished.
1828. Webster, Tropical. 2. Incident to the tropics; as, tropical diseases.
1843. R. J. Graves, Syst. Clin. Med., xi. 118. [Salivation] has been also very extensively recommended by army and navy surgeons, in the treatment of tropical fevers.
1893. A. Davidson, Hygiene & Dis. Warm Climates, xvii. 613. Tropical Liver.
1905. Daily Chron., 9 Oct., 5/3. The notorious disease known in Germany as ‘tropencholer,’ or tropical frenzy.
c. fig. Like the climate or growth of the tropics; very hot, ardent, or luxuriant.
1834. Tait’s Mag., I. 383/1. Home he came, after an absence of fifty years, in a hissing hot fit of tropical rage.
1850. S. Dobell, Roman, vi. Poet. Wks. (1875), 85. My fierce and tropical fancy, Hot with swift pulses.
1880. ‘Ouida,’ Moths, I. 174. We Russians have a passion for tropical houses.
Mod. The heat was perfectly tropical.
3. Zool. (transf. from 1 or 2.) Used to describe the position of certain spines in the skeleton of some radiolarians: see quot.
1888. Rolleston & Jackson, Anim. Life, 874, note. Imagine a globe with an axis of rotation, and five circles inscribed on it, an equatorial, two tropical and two polar. The twenty spines lie four in each of these circles, the equatorial and polar spines in the same meridian lines,… the tropical in meridian lines exactly intermediate.
4. Pertaining to, involving, or of the nature of a trope or tropes; metaphorical, figurative.
1567. Maplet, Gr. Forest, 97. To sende ouer Owles to Athens. In Tropicall sense, ment of such as bestow largely vpon them that haue no neede.
1620. T. Granger, Div. Logike, 19. Whether the words bee plaine, and proper, or tropicall, and figuratiue.
1646. Sir T. Browne, Pseud. Ep., III. iii. 111. A strict and literall acception of a loose and tropicall expression.
1725. Watts, Logic, I. iv. § 7. They are used in a figurative or tropical Sense, when they are made to signify some things, which only bear either a Reference or a Resemblance to the primary Ideas of them.
1819. G. S. Faber, Dispensations (1823), II. II. v. 190. The great sheet let down from heaven was as perfect a tropical hieroglyphic as any invented by the ingenuity of Moses.
1862. H. Spencer, First Princ., XV. (1875), 349. These [writings] had been partially differentiated into the kuriological or imitative, and the tropical or symbolic.
5. Math. ? Relating to the number of values of a function corresponding to one value of the variable.
1887. Cayley, Math. Papers, XII. 433. We wish to know whether u is a monotropic function of z. It will not be so if we have a tropical point,… such that [etc.].
