The Collaborative International Dictionary of English v.0.48:

encode \en*code"\ ([e^]n*k[=o]d"), v. t.
   To convert (a text, data) into a series of secret symbols by
   means of a code[5]; to encrypt.

   Syn: encrypt, code, encipher, cipher, cypher, inscribe, write
        in code.
        [PJC]

WordNet (r) 3.0 (2006):

encode
    v 1: convert information into code; "encode pictures digitally"
         [ant: decipher, decode, decrypt]

The Free On-line Dictionary of Computing (30 December 2018):

encode

   1.  To convert data or some physical
   quantity into a given format.  E.g. uuencode.

   See also encoder.

   2.  To encrypt, to perform encryption.

   (1999-07-06)