Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. Any of various organic compounds normally with basic chemical properties and usually containing at least one nitrogen atom in a heterocyclic ring, occurring chiefly in many vascular plants and some fungi. Many alkaloids, such as nicotine, quinine, cocaine, and morphine, are known for their poisonous or medicinal attributes.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Any of many organic heterocyclic bases, that occur in nature and often have medicinal properties.
  • adj. Relating to, resembling, or containing alkali.

from the GNU version of the Collaborative International Dictionary of English

  • adj. Pertaining to, resembling, or containing, alkali.
  • adj. of or pertaining to alkaloids.
  • n. An organic base, especially one of a class of nitrogen-containing substances occurring ready formed in the tissues of plants and the bodies of animals.

from The Century Dictionary and Cyclopedia

  • n. A body resembling an alkali in properties; one of a class of nitrogenous compounds which occur in plants in combination with organic acids, and are sometimes called the organic bases of plants, as morphine, nicotine, quinine, etc.
  • Relating to or containing alkali.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. natural bases containing nitrogen found in plants

Etymologies

alkal(i) + -oid.
(American Heritage® Dictionary of the English Language, Fourth Edition)
alkali +‎ -oid. Compare French alcaloïde. (Wiktionary)

Examples

  • Aconite root contains about 0.4 per cent. of alkaloid and one-fifteenth of a grain of the alkaloid is a lethal dose.

    The Witch-cult in Western Europe A Study in Anthropology

  • According to Grupe Dr. Pina used this substance with great success in the treatment of malarial fevers, but neither Grupe's report nor Pina's experiment are of any scientific value, inasmuch as they have neglected to mention the doses in which the so-called alkaloid was employed.

    The Medicinal Plants of the Philippines

  • Cocaine is an alkaloid which is contained in the Erythroxylon coca which grows in the Andes mountains of Peru and Bolivia 1000 to 3000 m. above sea level. 1 The first use of cocaine in history was by the Peruvian Indians in the 6th century who chewed on the coca leaves for the sense of wellness and endurance which it produced and who believed it to be a part of the Inca religion. 2

    Cocaine Toxicity

  • Many forms of D. dumetorum contain a convulsant alkaloid which is a mixture of stereoisomers of dihydrodioscorine.

    Chapter 37

  • Coffee, tea and chocolate contain a poisonous alkaloid which is generally called caffeine.

    Maintaining Health Formerly Health and Efficiency

  • This is a volatile alkaloid which is not poisonous, and is thought to be almost identical with ammonia.

    Herbal Simples Approved for Modern Uses of Cure

  • A crystalline alkaloid which is fatal to frogs in a dose of one centigramme, has been isolated from the common Stinging Nettle.

    Herbal Simples Approved for Modern Uses of Cure

  • 'Such doings, young man,' said I. 'I've read,' said I, 'that some German -- I've forgotten his name -- has created from the human brain a new kind of alkaloid, idiotine.'

    The Wife, and other stories

  • "Amanitin is a wonderful and dangerous alkaloid, which is absorbed in the intestinal canal.

    The Treasure-Train

  • I’ve forgotten his name — has created from the human brain a new kind of alkaloid, idiotine.’

    The Wife

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