The Collaborative International Dictionary of English v.0.48:

Substitute \Sub"stit"ute\, n. [L. substitutus, p. p. of
   substituere to put under, put in the place of; sub under +
   statuere to put, place: cf. F. substitut. See Statute.]
   One who, or that which, is substituted or put in the place of
   another; one who acts for another; that which stands in lieu
   of something else; specifically (Mil.), a person who enlists
   for military service in the place of a conscript or drafted
   man.
   [1913 Webster]

         Hast thou not made me here thy substitute? --Milton.
   [1913 Webster]

         Ladies [in Shakespeare's age] . . . wore masks as the
         sole substitute known to our ancestors for the modern
         parasol.                                 --De Quincey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Substitute \Sub"stit"ute\, v. t. [imp. & p. p. Substituted; p.
   pr. & vb. n. Substituting.] [See Substitute, n.]
   To put in the place of another person or thing; to exchange.
   [1913 Webster]

         Some few verses are inserted or substituted in the room
         of others.                               --Congreve.
   [1913 Webster]

WordNet (r) 3.0 (2006):

substitute
    adj 1: capable of substituting in any of several positions on a
           team; "a utility infielder" [syn: utility(a),
           substitute(a)]
    2: serving or used in place of another; "an alternative plan"
       [syn: alternate, alternative, substitute]
    3: artificial and inferior; "ersatz coffee"; "substitute coffee"
       [syn: ersatz, substitute]
    n 1: a person or thing that takes or can take the place of
         another [syn: substitute, replacement]
    2: an athlete who plays only when a starter on the team is
       replaced [syn: substitute, reserve, second-stringer]
    3: someone who takes the place of another (as when things get
       dangerous or difficult); "the star had a stand-in for
       dangerous scenes"; "we need extra employees for summer fill-
       ins" [syn: stand-in, substitute, relief, reliever,
       backup, backup man, fill-in]
    v 1: put in the place of another; switch seemingly equivalent
         items; "the con artist replaced the original with a fake
         Rembrandt"; "substitute regular milk with fat-free milk";
         "synonyms can be interchanged without a changing the
         context's meaning" [syn: substitute, replace,
         interchange, exchange]
    2: be a substitute; "The young teacher had to substitute for the
       sick colleague"; "The skim milk substitutes for cream--we are
       on a strict diet" [syn: substitute, sub, stand in,
       fill in]
    3: act as a substitute; "She stood in for the soprano who
       suffered from a cold" [syn: substitute, deputize,
       deputise, step in]

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

Substitute
SUB

    (SUB) ASCII character 26.

   [Why?]

   (1996-06-28)