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.]

The Collaborative International Dictionary of English v.0.48:

Cohort \Co"hort\, n. [L. cohors, prop. an inclosure: cf. F.
   cohorte. See Court, n.]
   1. (Rom. Antiq.) A body of about five or six hundred
      soldiers; the tenth part of a legion.
      [1913 Webster]

   2. Any band or body of warriors.
      [1913 Webster]

            With him the cohort bright
            Of watchful cherubim.                 --Milton.
      [1913 Webster]

   3. (Bot.) A natural group of orders of plants, less
      comprehensive than a class.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cohort
    n 1: a company of companions or supporters
    2: a band of warriors (originally a unit of a Roman Legion)
    3: a group of people having approximately the same age [syn:
       age group, age bracket, cohort]

Moby Thesaurus II by Grady Ward, 1.0:

124 Moby Thesaurus words for "cohort":
   KP, abettor, accessory, accomplice, accomplice in crime, adherent,
   adjunct, age group, ally, army, army group, associate, attendance,
   attendant, band, battalion, battery, battle group, bedfellow, bevy,
   body, body of retainers, brigade, brother, brother-in-arms, bunch,
   cabal, cadre, cast, clique, coadjutor, coconspirator, colleague,
   column, combat command, combat team, companion, company,
   compatriot, compeer, complement, comrade, confederate, confrere,
   consociate, consort, contingent, copartner, corps, cortege,
   coterie, court, covey, crew, crony, crowd, detachment, detail,
   disciple, division, entourage, faction, fellow, fellow conspirator,
   fellow member, field army, field train, file, fleet, flying column,
   follower, following, friend, gang, garrison, group, grouping,
   groupment, henchman, in-group, junta, kitchen police, legion,
   maniple, mate, mob, movement, organization, out-group, outfit,
   pack, parasite, pard, partisan, party, peer group, phalanx,
   platoon, posse, rank, regiment, retinue, rout, salon, satellite,
   sectary, section, set, socius criminis, squad, squadron, stable,
   string, suite, supporter, tactical unit, task force, team, train,
   tribe, troop, troupe, unit, wing