The Collaborative International Dictionary of English v.0.48:

Every \Ev"er*y\, a. & a. pron. [OE. everich, everilk; AS.
   [=ae]fre ever + [ae]lc each. See Ever, each.]
   1. All the parts which compose a whole collection or
      aggregate number, considered in their individuality, all
      taken separately one by one, out of an indefinite number.
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            Every man at his best state is altogether vanity.
                                                  --Ps. xxxix.
                                                  5.
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            Every door and window was adorned with wreaths of
            flowers.                              --Macaulay.
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   2. Every one. Cf. Each. [Obs.] "Every of your wishes."
      --Shak.
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            Daily occasions given to every of us. --Hooker.
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   Every each, every one. [Obs.] "Every each of them hath some
      vices." --Burton..

   Every now and then, at short intervals; occasionally;
      repeatedly; frequently. [Colloq.]
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   Note: Every may, by way of emphasis, precede the article the
         with a superlative adjective; as, every, the least
         variation. --Locke.

   Syn: Every, Each, Any.

   Usage: Any denotes one, or some, taken indifferently from the
          individuals which compose a class. Every differs from
          each in giving less prominence to the selection of the
          individual. Each relates to two or more individuals of
          a class. It refers definitely to every one of them,
          denoting that they are considered separately, one by
          one, all being included; as, each soldier was
          receiving a dollar per day. Every relates to more than
          two and brings into greater prominence the notion that
          not one of all considered is excepted; as, every
          soldier was on service, except the cavalry, that is,
          all the soldiers, etc.
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                In each division there were four pentecosties,
                in every pentecosty four enomoties, and of each
                enomoty there fought in the front rank four
                [soldiers].                       --Jowett
                                                  (Thucyd. ).
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                If society is to be kept together and the
                children of Adam to be saved from setting up
                each for himself with every one else his foe.
                                                  --J. H.
                                                  Newman.
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WordNet (r) 3.0 (2006):

every now and then
    adv 1: occasionally; "every so often she visits her father"
           [syn: every so often, every now and then]