The Collaborative International Dictionary of English v.0.48:

Tier \Ti"er\, n.
   One who, or that which, ties.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tier \Ti"er\, n. [See Tire a headdress.]
   A chold's apron covering the upper part of the body, and tied
   with tape or cord; a pinafore. [Written also tire.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tier \Tier\, n. [Perhaps fr. OF. tire, F. tire; probably of
   Teutonic origin; cf. OHG. ziar[imac] ornament, G. zier, AS.
   t[imac]r glory, ti['e]r row, rank. But cf. also F. tirer to
   draw, pull; of Teutonic origin. Cf. Attire, v. t., Tire a
   headdress, but also Tirade.]
   A row or rank, especially one of two or more rows placed one
   above, or higher than, another; as, a tier of seats in a
   theater.
   [1913 Webster]

   Tiers of a cable, the ranges of fakes, or windings, of a
      cable, laid one within another when coiled.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tier
    n 1: a relative position or degree of value in a graded group;
         "lumber of the highest grade" [syn: grade, level,
         tier]
    2: any one of two or more competitors who tie one another
    3: a worker who ties something [syn: tier, tier up]
    4: something that is used for tying; "the sail is fastened to
       the yard with tiers"
    5: one of two or more layers one atop another; "tier upon tier
       of huge casks"; "a three-tier wedding cake"

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "tier":
   Indian file, array, articulation, band, bank, bed, bedding, belt,
   buzz, category, catena, catenation, chain, chain reaction,
   chaining, concatenation, connection, consecution, continuum,
   couche, course, cycle, deck, descent, drone, echelon, endless belt,
   endless round, file, filiation, floor, gallery, gamut, gradation,
   grade, group, grouping, hum, layer, league, ledge, level, line,
   lineage, measures, monotone, nexus, order, overlayer, overstory,
   pendulum, periodicity, pigeonhole, plenum, powder train,
   progression, queue, range, rank, recurrence, reticulation,
   rotation, round, routine, row, run, scale, seam, sequence, series,
   shelf, single file, spectrum, stage, step, story, stratum, string,
   substratum, succession, superstratum, swath, thickness, thread,
   topsoil, train, underlayer, understory, understratum, windrow,
   zone