The Collaborative International Dictionary of English v.0.48:

Preliminary \Pre*lim"i*na*ry\, a. [Pref. pre + L. liminaris
   belonging to a threshold, fr. limen, liminis, threshold,
   entrance: cf. F. pr['e]liminaire. Cf. Limit.]
   Introductory; previous; preceding the main discourse or
   business; prefatory; as, preliminary observations to a
   discourse or book; preliminary articles to a treaty;
   preliminary measures; preliminary examinations.
   [1913 Webster]

   Syn: Introductory; preparatory; prefatory; proemial;
        previous; prior; precedent; antecedent.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Preliminary \Pre*lim"i*na*ry\, n.; pl. Preliminaries.
   That which precedes the main discourse, work, design, or
   business; something introductory or preparatory; as, the
   preliminaries to a negotiation or duel; to take one's
   preliminaries the year before entering college.
   [1913 Webster]

   Syn: Introduction; preface; prelude.
        [1913 Webster]

WordNet (r) 3.0 (2006):

preliminary
    adj 1: denoting an action or event preceding or in preparation
           for something more important; designed to orient or
           acquaint with a situation before proceeding; "a
           preliminary investigation"
    n 1: a minor match preceding the main event [syn: preliminary,
         prelim]
    2: something that serves as a preceding event or introduces what
       follows; "training is a necessary preliminary to employment";
       "drinks were the overture to dinner" [syn: preliminary,
       overture, prelude]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "preliminary":
   advance, advanced, antecedent, anterior, arrangement, avant-garde,
   avant-propos, basic training, beginning, breakthrough, briefing,
   chief, clearing the decks, coming out, curtain raiser, debut,
   embarkation, embarkment, equipment, exordial, exordium,
   exploratory, familiarization, first, first appearance, fixing,
   floating, flotation, foremost, forerunning, foreword, foundation,
   front matter, frontispiece, groundwork, headmost, inaugural,
   inaugural address, inauguration, induction, initial, initiation,
   initiatory, innovation, installation, installment, introduction,
   introductory, launching, leading, leap, maiden speech, makeready,
   making ready, manufacture, mobilization, opener, opening, original,
   overture, planning, postulate, preamble, prearrangement,
   precedence, precedent, preceding, precessional, precursory,
   preface, prefatory, prefix, prefixed, prefixture, preliminaries,
   preliminary act, preliminary step, prelude, preludial, prelusive,
   premise, premonitory, prep, preparation, preparatory,
   preparatory study, preparing, prepositive, prepping, prerequisite,
   presupposition, pretreatment, prevenient, prior, processing,
   prodromal, prodrome, prodromic, proem, proemial, prolegomena,
   prolegomenon, prolepsis, prologue, propaedeutic, protasis,
   provision, readying, spadework, training, treatment, trial, tryout,
   unveiling, verse, voluntary, warm-up



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRELIMINARY. Something which precedes, as preliminaries of peace, which are
the first sketch of a treaty, and contain the principal articles on which
both parties are desirous of concluding, and which are to serve as the basis
of the treaty.