The Collaborative International Dictionary of English v.0.48:

Toot \Toot\, v. i. [imp. & p. p. Tooted; p. pr. & vb. n.
   Tooting.] [Cf. D. toeten to blow a horn, G. tuten, Sw.
   tuta, Dan. tude; probably of imitative origin.]
   To blow or sound a horn; to make similar noise by contact of
   the tongue with the root of the upper teeth at the beginning
   and end of the sound; also, to give forth such a sound, as a
   horn when blown. "A tooting horn." --Howell.
   [1913 Webster]

         Tooting horns and rattling teams of mail coaches.
                                                  --Thackeray.
   [1913 Webster]