from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Having or marked by repeated cycles.
  • adjective Happening or appearing regularly or from time to time.
  • adjective Characterized by periodic sentences.

from The Century Dictionary.

  • Noting an acid, a substance produced by the interaction of iodine and aqueous perchloric acid, known only in crystals which contain two molecules of water: HIO4.2H2O. Its solution has a strong acid reaction and it forms several distinct series of salts.
  • In mathematics, with values which recur as the value of the independent variable continuously increases.
  • Pertaining to or of the nature of a period, cycle, or round of years or events.
  • Performed or proceeding in a series of successive circuits or revolutions: as, the periodic motions of the planets round the sun, or of the moon round the earth.
  • Happening or occurring at regularly recurring intervals of time; statedly recurring; as, a periodic publication; the periodic return of a plant's flowering; periodic outbursts; the periodic character of ague; the periodic motion of a vibrating tuniug-fork or musical string.
  • In rhetoric: Of or pertaining to a period or complete sentence; complete in grammatical structure.
  • Noting that form of sentence in which the sense is incomplete or suspended until the end is reached.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective (Chem.) Pertaining to, derived from, or designating, the highest oxygen acid (HIO�) of iodine.
  • adjective Of or pertaining to a period or periods, or to division by periods.
  • adjective Performed in a period, or regular revolution; proceeding in a series of successive circuits.
  • adjective Happening, by revolution, at a stated time; returning regularly, after a certain period of time; acting, happening, or appearing, at fixed intervals; recurring.
  • adjective (Rhet.) Of or pertaining to a period; constituting a complete sentence.
  • adjective (Astron.) a comet that moves about the sun in an elliptic orbit; a comet that has been seen at two of its approaches to the sun.
  • adjective (Math.) a function whose values recur at fixed intervals as the variable uniformly increases. The trigonomertic functions, as sin x, tan x, etc., are periodic functions. Exponential functions are also periodic, having an imaginary period, and the elliptic functions have not only a real but an imaginary period, and are hence called doubly periodic.
  • adjective (Chem.) the generalization that the properties of the chemical elements are periodic functions of their atomic wieghts. “In other words, if the elements are grouped in the order of their atomic weights, it will be found that nearly the same properties recur periodically throughout the entire series.” The following tabular arrangement of the atomic weights shows the regular recurrence of groups (under I., II., III., IV., etc.), each consisting of members of the same natural family. The gaps in the table indicate the probable existence of unknown elements.
  • adjective (Astron.) a variable star whose changes of brightness recur at fixed periods.
  • adjective (Astron.) the time of a complete revolution of the body about the sun, or of a satellite about its primary.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Relative to a period or periods.
  • adjective Having repeated cycles.
  • adjective Occurring at regular intervals.
  • adjective Pertaining to the revolution of a celestial object in its orbit.
  • adjective periodical
  • adjective rhetoric Having a structure characterized by periodic sentences.
  • adjective mathematics for which any return to it must occur in multiples of time steps, for some .
  • adjective Of or derived from a periodic acid.

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

  • adjective happening or recurring at regular intervals
  • adjective recurring or reappearing from time to time


from Wiktionary, Creative Commons Attribution/Share-Alike License

From French périodique, from Medieval Latin periodicus ("cyclical"), from Latin periodus ("complete sentence, period, circuit"), from Ancient Greek περίοδος (periodos, "cycle, period of time").

from Wiktionary, Creative Commons Attribution/Share-Alike License

per- +‎ iodic


  • The subsequent section focuses on the opportunity to restructure significantly the sequence, number, and duration of prototyping cycles into what we refer to as a periodic pattern of prototyping.

    Managing New Product and Process Development

  • Alcatel-Lucent, the French maker of telephone network equipment, said Thursday that it planned to cut 3.4 percent of its workforce in France by the end of the year as part of what it described as a periodic review of its personnel needs.

    NYT > Home Page

  • He has particular research interests in periodic limb movements in sleep (PLMS), and has received a mentored patient-oriented research career development award (K23), through the National Center for Research Resources of the National Institutes of Health, entitled "Periodic Limb Movements in Williams Syndrome".

    Sleep disorders research

  • It was like watching a geyser go off, the way it would jet out in periodic rushes.

    Being Critical : Bev Vincent

  • No country that presides over a barbarous occupation, has apartheid laws, engages in periodic genocidal rampages, and elects Zionist ultras such as Netanyahu and Avigdor (Death to Arabs) Liebermann to power has the right to point the finger at anyone else.

    Global Voices in English » Israel: Reflections on the Holocaust Memorial Day and Durban II

  • As a long-term periodic non-sleeper, I greeted this news with a "Yes, and?"

    Sharon Glassman: Why Can't Women Sleep? Part II: How to Sleep Well on Sunday Night

  • Levees along the Mississippi have prevented silt from depositing in periodic floods, resulting in subsidence and loss of land throughout the Delta.

    Rebuilding New Orleans? « BuzzMachine

  • The FEC requires candidates to disclose their expenditures, including any payments to bloggers, in periodic reports to the government.

    May 2005

  • Signatories continue to meet in periodic Conferences of the Parties, of which the most significant to date occurred in Kyoto in 1997, when binding emissions reductions for industrialized countries were proposed under an agreement called the Kyoto Protocol.

    Breaking the Global-Warming Gridlock

  • Signatories continue to meet in periodic Conferences of the Parties, of which the most significant to date occurred in Kyoto in 1997, when binding emissions reductions for industrialized countries were proposed under an agreement called the Kyoto Protocol.

    Breaking the Global-Warming Gridlock


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  • PEER ee Odd ick - happening at regular intervals

    PURR eye Odd ick - having iodine substituends for all hydrogen atoms

    May 2, 2008

  • Someone's got a list somewhere for words that are spelt the same and pronounced differently.

    May 2, 2008

  • Having written it I realise that pronounced could be on it but I searched and it isn't.

    May 2, 2008