Source : Webster's Revised Unabridged Dictionary (1913)

Tilde \Til"de\, n. [Sp., fr. L. titulus a superscription, title,
   token, sign. See {Title}, n.]
   The accentual mark placed over n, and sometimes over l, in
   Spanish words [thus, [~n], [~l]], indicating that, in
   pronunciation, the sound of the following vowel is to be
   preceded by that of the initial, or consonantal, y.

Source : WordNet®

tilde
     n : a diacritical mark (~) placed over the letter n in Spanish
         to indicate a palatal nasal sound or over a vowel in
         Portuguese to indicate nasalization

Source : Free On-Line Dictionary of Computing

tilde
     
         "~" {ASCII} character 126.
     
        Common names are: {ITU-T}: tilde; squiggle; {twiddle}; not.
        Rare: approx; wiggle; {swung dash}; enyay; {INTERCAL}: sqiggle
        (sic).
     
        Used as {C}'s prefix {bitwise negation} {operator}; and in
        {Unix} {csh}, {GNU Emacs}, and elsewhere, to stand for the
        current user's {home directory}, or, when prefixed to a {login
        name}, for the given user's home directory.
     
        The "swung dash" or "approximation" sign is not quite the same
        as {tilde} in typeset material but the ASCII tilde serves for
        both (compare {angle brackets}).
     
        [Has anyone else heard this called "tidal" (as in wave)?]
     
        (1996-10-18)