The Collaborative International Dictionary of English v.0.48:

Profession \Pro*fes"sion\, n. [F., fr. L. professio. See
   Profess, v.]
   1. The act of professing or claiming; open declaration;
      public avowal or acknowledgment; as, professions of
      friendship; a profession of faith.
      [1913 Webster]

            A solemn vow, promise, and profession. --Bk. of Com.
                                                  Prayer.
      [1913 Webster]

   2. That which one professed; a declaration; an avowal; a
      claim; as, his professions are insincere.
      [1913 Webster]

            The Indians quickly perceive the coincidence or the
            contradiction between professions and conduct. --J.
                                                  Morse.
      [1913 Webster]

   3. That of which one professed knowledge; the occupation, if
      not mechanical, agricultural, or the like, to which one
      devotes one's self; the business which one professes to
      understand, and to follow for subsistence; calling;
      vocation; employment; as, the profession of arms; the
      profession of a clergyman, lawyer, or physician; the
      profession of lecturer on chemistry.
      [1913 Webster]

            Hi tried five or six professions in turn.
                                                  --Macaulay.
      [1913 Webster]

   Note: The three professions, or learned professions, are,
         especially, theology, law, and medicine.
         [1913 Webster]

   4. The collective body of persons engaged in a calling; as,
      the profession distrust him.
      [1913 Webster]

   5. (Eccl. Law.) The act of entering, or becoming a member of,
      a religious order.
      [1913 Webster]

WordNet (r) 3.0 (2006):

profession
    n 1: the body of people in a learned occupation; "the news
         spread rapidly through the medical profession"; "they
         formed a community of scientists"
    2: an occupation requiring special education (especially in the
       liberal arts or sciences)
    3: an open avowal (true or false) of some belief or opinion; "a
       profession of disagreement" [syn: profession, professing]
    4: affirmation of acceptance of some religion or faith; "a
       profession of Christianity"

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "profession":
   acceptance, acknowledgment, admission, affidavit, affirmance,
   affirmation, allegation, allowance, announcement, annunciation,
   appreciation, art, assertion, asseveration, attest, attestation,
   averment, avouchment, avowal, business, calling, career,
   career building, careerism, claim, compurgation, concession,
   conclusion, confession, confession of faith, craft, creed,
   declaration, declaration of faith, deposition, dictum, disclosure,
   employment, enunciation, field, game, handicraft,
   instrument in proof, ipse dixit, job, legal evidence, lifework,
   line, line of business, line of work, manifesto, metier, mission,
   mystery, number, occupation, position, position paper,
   positive declaration, post, practice, predicate, predication,
   proclamation, pronouncement, proposition, protest, protestation,
   pursuit, racket, recognition, say, say-so, saying, situation,
   specialization, specialty, sphere, stance, stand, statement,
   sworn evidence, sworn statement, sworn testimony, testimonial,
   testimonium, testimony, trade, utterance, vocation, vouch, walk,
   walk of life, witness, word, work



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

PROFESSION. This word has several significations. 1. It is a public
declaration respecting something. Code, 10, 41, 6.
     2. It i's a state, art, or mystery; as the legal profession. Dig. 1,
18, 6, 4; Domat, Dr. Pub. 1. 1, t. 9, s. 1, n. 7. 3. In the ecclesiastical
law, it is the act of entering into a religious order. See 17 Vin. Ab. 545.