The Collaborative International Dictionary of English v.0.48:

Mediocre \Me"di*o`cre\, n.
   1. A mediocre person; a mediocrity. [R.]
      [1913 Webster]

   2. A young monk who was excused from performing a portion of
      a monk's duties. --Shipley.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

mediocre \me`di*o"cre\ (m[=e]`d[i^]*[=o]"k[~e]r), a. [F.
   m['e]diocre, L. mediocris, fr. medius middle. See Mid.]
   Of a middle quality; of but a moderate or low degree of
   excellence; indifferent; ordinary. " A very mediocre poet."
   --Pope.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mediocre
    adj 1: moderate to inferior in quality; "they improved the
           quality from mediocre to above average" [syn: mediocre,
           second-rate]
    2: lacking exceptional quality or ability; "a novel of average
       merit"; "only a fair performance of the sonata"; "in fair
       health"; "the caliber of the students has gone from mediocre
       to above average"; "the performance was middling at best"
       [syn: average, fair, mediocre, middling]
    3: poor to middling in quality; "there have been good and
       mediocre and bad artists"

Moby Thesaurus II by Grady Ward, 1.0:

136 Moby Thesaurus words for "mediocre":
   adulterated, amidships, artless, average, bad, banal, base,
   betwixt and between, blemished, central, common, commonplace, core,
   damaged, defective, deficient, dull, equatorial, equidistant,
   erroneous, everyday, fair, fair to middling, fairish, fallible,
   faulty, found wanting, garden-variety, half-assed, halfway,
   immature, impaired, imperfect, imprecise, impure, inaccurate,
   inadept, inadequate, inapt, inattentive, incompetent, incomplete,
   indifferent, inefficient, inept, inexact, inexpert, inferior,
   insipid, insufficient, interior, intermediary, intermediate,
   lacking, lackluster, little, makeshift, maladroit, mean, medial,
   median, mediterranean, medium, mesial, mezzo, mid, middle,
   middle-of-the-road, middlemost, middling, midland, midmost,
   midships, midway, mixed, moderate, modest, namby-pamby,
   no great shakes, normal, not bad, not comparable, not in it,
   not perfect, nuclear, of a kind, of a sort, of sorts, off,
   ordinary, out of it, partial, passable, patchy, pedestrian, petty,
   poor, respectable, routine, run-of-the-mill, second-rate, shabby,
   short, sketchy, skill-less, small, so so, so-so, standard, tedious,
   third-rate, thoughtless, tolerable, trivial, unapt, undeft,
   undeveloped, undexterous, undextrous, undistinguished, uneven,
   unexceptional, unfacile, unfinished, unimaginative, uninspired,
   unintelligent, unperfected, unproficient, unskillful, unsound,
   unthorough, usual, vapid, wanting, wishy-washy