The Collaborative International Dictionary of English v.0.48:

Series \Se"ries\, n. [L. series, fr. serere, sertum, to join or
   bind together; cf. Gr. ??? to fasten, Skr. sarit thread. Cf.
   Assert, Desert a solitude, Exert, Insert,
   Seraglio.]
   1. A number of things or events standing or succeeding in
      order, and connected by a like relation; sequence; order;
      course; a succession of things; as, a continuous series of
      calamitous events.
      [1913 Webster]

            During some years his life a series of triumphs.
                                                  --Macaulay.
      [1913 Webster]

   2. (Biol.) Any comprehensive group of animals or plants
      including several subordinate related groups.
      [1913 Webster]

   Note: Sometimes a series includes several classes; sometimes
         only orders or families; in other cases only species.
         [1913 Webster]

   3. (Bot.) In Engler's system of plant classification, a group
      of families showing certain structural or morphological
      relationships. It corresponds to the cohort of some
      writers, and to the order of many modern systematists.
      [Webster 1913 Suppl.]

   4. (Math.) An indefinite number of terms succeeding one
      another, each of which is derived from one or more of the
      preceding by a fixed law, called the law of the series;
      as, an arithmetical series; a geometrical series.
      [1913 Webster]

   5. (Elec.) A mode of arranging the separate parts of a
      circuit by connecting them successively end to end to form
      a single path for the current; -- opposed to parallel.
      The parts so arranged are said to be

   in series.
      [Webster 1913 Suppl.]

   6. (Com.) A parcel of rough diamonds of assorted qualities.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

series
    n 1: similar things placed in order or happening one after
         another; "they were investigating a series of bank
         robberies"
    2: a serialized set of programs; "a comedy series"; "the
       Masterworks concert series" [syn: serial, series]
    3: a periodical that appears at scheduled times [syn: series,
       serial, serial publication]
    4: (sports) several contests played successively by the same
       teams; "the visiting team swept the series"
    5: (electronics) connection of components in such a manner that
       current flows first through one and then through the other;
       "the voltage divider consisted of a series of fixed
       resistors"
    6: a group of postage stamps having a common theme or a group of
       coins or currency selected as a group for study or
       collection; "the Post Office issued a series commemorating
       famous American entertainers"; "his coin collection included
       the complete series of Indian-head pennies"
    7: (mathematics) the sum of a finite or infinite sequence of
       expressions