The Collaborative International Dictionary of English v.0.48:

Alter \Al"ter\, v. i.
   To become, in some respects, different; to vary; to change;
   as, the weather alters almost daily; rocks or minerals alter
   by exposure. "The law of the Medes and Persians, which
   altereth not." --Dan. vi. 8.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Alter \Al"ter\, v. t. [imp. & p. p. Altered; p. pr. & vb. n.
   Altering.] [F. alt['e]rer, LL. alterare, fr. L. alter
   other, alius other. Cf. Else, Other.]
   1. To make otherwise; to change in some respect, either
      partially or wholly; to vary; to modify. "To alter the
      king's course." "To alter the condition of a man." "No
      power in Venice can alter a decree." --Shak.
      [1913 Webster]

            It gilds all objects, but it alters none. --Pope.
      [1913 Webster]

            My covenant will I not break, nor alter the thing
            that is gone out of my lips.          --Ps. lxxxix.
                                                  34.
      [1913 Webster]

   2. To agitate; to affect mentally. [Obs.] --Milton.
      [1913 Webster]

   3. To geld. [Colloq.]
      [1913 Webster]

   Syn: Change, Alter.

   Usage: Change is generic and the stronger term. It may
          express a loss of identity, or the substitution of one
          thing in place of another; alter commonly expresses a
          partial change, or a change in form or details without
          destroying identity.
          [1913 Webster]

WordNet (r) 3.0 (2006):

alter
    v 1: cause to change; make different; cause a transformation;
         "The advent of the automobile may have altered the growth
         pattern of the city"; "The discussion has changed my
         thinking about the issue" [syn: change, alter,
         modify]
    2: become different in some particular way, without permanently
       losing one's or its former characteristics or essence; "her
       mood changes in accordance with the weather"; "The
       supermarket's selection of vegetables varies according to the
       season" [syn: change, alter, vary]
    3: make an alteration to; "This dress needs to be altered"
    4: insert words into texts, often falsifying it thereby [syn:
       interpolate, alter, falsify]
    5: remove the ovaries of; "Is your cat spayed?" [syn: alter,
       neuter, spay, castrate]

The Free On-line Dictionary of Computing (19 January 2023):

ALTER

    An SQL Data Definition Language command that
   adds or removes columns or indexes to/from a table or
   modifies the table definition in some other way.  This differs
   from the INSERT, UPDATE and DELETE (Data Modification
   Language) commands in that those change the data stored in
   the table but not its definition.

   MySQL ALTER TABLE command
   (http://dev.mysql.com/doc/refman/5.1/en/alter-table.html).

   (2009-11-10)