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

  • Three: trilobate.
  • Occurring at intervals of three: trimonthly.
  • Occurring three times during: triweekly.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • three
  • Used in combination with a known element name (e.g. 'tri-silicon') to designate an unknown element that would reside three periods lower than the known element on a Mendeleev-type periodic table. See Mendeleev's predicted elements.

from the GNU version of the Collaborative International Dictionary of English

  • A prefix meaning three, thrice, threefold; as in tricolored, tridentate.
  • A prefix (also used adjectively) denoting three proportional or combining part, or the third degree of that to the name of which it is prefixed; as in trisulphide, trioxide, trichloride.

from The Century Dictionary and Cyclopedia

  • n. Specifically, in chem., a prefix to the names of compounds containing three atoms or combining units of some particular element or radical, as sulphur trioxid, SO3, and triethylamine, N(C2H5)3.
  • n. A prefix of Latin and Greek origin, meaning ‘three.’


Middle English, from Latin and Greek; see trei- in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin tres ("three") and Ancient Greek τρία (tria, "three"). (Wiktionary)
From Sanskrit  (tri-, "three"). (Wiktionary)



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