The Collaborative International Dictionary of English v.0.48:

Lesson \Les"son\, v. t. [imp. & p. p. Lessoned (-s'nd); p. pr.
   & vb. n. Lessoning.]
   To teach; to instruct. --Shak.
   [1913 Webster]

         To rest the weary, and to soothe the sad,
         Doth lesson happier men, and shame at least the bad.
                                                  --Byron.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lesson \Les"son\ (l[e^]s"s'n), n. [OE. lessoun, F. le[,c]on
   lesson, reading, fr. L. lectio a reading, fr. legere to read,
   collect. See Legend, and cf. Lection.]
   1. Anything read or recited to a teacher by a pupil or
      learner; something, as a portion of a book, assigned to a
      pupil to be studied or learned at one time.
      [1913 Webster]

   2. That which is learned or taught by an express effort;
      instruction derived from precept, experience, observation,
      or deduction; a precept; a doctrine; as, to take or give a
      lesson in drawing." A smooth and pleasing lesson."
      --Milton.
      [1913 Webster]

            Emprinteth well this lesson in your mind. --Chaucer.
      [1913 Webster]

   3. A portion of Scripture read in divine service for
      instruction; as, here endeth the first lesson.
      [1913 Webster]

   4. A severe lecture; reproof; rebuke; warning.
      [1913 Webster]

            She would give her a lesson for walking so late.
                                                  --Sir. P.
                                                  Sidney.
      [1913 Webster]

   5. (Mus.) An exercise; a composition serving an educational
      purpose; a study.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lesson
    n 1: a unit of instruction; "he took driving lessons"
    2: punishment intended as a warning to others; "they decided to
       make an example of him" [syn: example, deterrent example,
       lesson, object lesson]
    3: the significance of a story or event; "the moral of the story
       is to love thy neighbor" [syn: moral, lesson]
    4: a task assigned for individual study; "he did the lesson for
       today"

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "lesson":
   admonish, admonishment, admonition, alarm, assignment, call down,
   castigation, caution, caveat, chalk talk, chastening, chastisement,
   chide, chiding, class, correction, deterrent, deterrent example,
   discouragement, discourse, disquisition, drill, example, exemplar,
   exercise, exposition, final notice, final warning, guide, harangue,
   hint, homework, homily, instruction, lecture,
   lecture-demonstration, maxim, message, model, monition, moral,
   moral lesson, morality, moralization, notice, notification,
   object lesson, objurgation, paragon, practice, preachment, precept,
   punishment, rating, reading, rebuke, recital, recitation,
   reprehension, reprimand, reproach, reprobation, reproof, reproval,
   schooling, scolding, sermon, session, set task, skull session,
   spanking, study, talk, task, teaching, threat, tick off, tip-off,
   tutoring, ultimatum, upbraiding, verbum sapienti, warning,
   warning piece