The Collaborative International Dictionary of English v.0.48:

Popular \Pop"u*lar\, a. [L. popularis, fr. populus people: cf.
   F. populaire. See People.]
   1. Of or pertaining to the common people, or to the whole
      body of the people, as distinguished from a select
      portion; as, the popular voice; popular elections.
      "Popular states." --Bacon. "So the popular vote inclines."
      --Milton.
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            The men commonly held in popular estimation are
            greatest at a distance.               --J. H.
                                                  Newman.
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   2. Suitable to common people; easy to be comprehended; not
      abstruse; familiar; plain.
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            Homilies are plain popular instructions. --Hooker.
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   3. Adapted to the means of the common people; possessed or
      obtainable by the many; hence, cheap; common; ordinary;
      inferior; as, popular prices; popular amusements.
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            The smallest figs, called popular figs, . . . are,
            of all others, the basest and of least account.
                                                  --Holland.
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   4. Beloved or approved by the people; pleasing to people in
      general, or to many people; as, a popular preacher; a
      popular law; a popular administration.
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   5. Devoted to the common people; studious of the favor of the
      populace. [R.]
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            Such popular humanity is treason.     --Addison.
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   6. Prevailing among the people; epidemic; as, a popular
      disease. [Obs.] --Johnson.
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   Popular action (Law), an action in which any person may sue
      for penalty imposed by statute. --Blackstone.
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Bouvier's Law Dictionary, Revised 6th Ed (1856):

POPULAR ACTION, punishment. An action given by statute to any one who will
sue for the penalty. A qui tam action. Dig. 47, 23, 1.