touch \touch\, v. i.
   1. to be in contact; to be in a state of junction, so that no
      space is between; as, two spheres touch only at points.
      --johnson.
      1913 webster

   2. to fasten; to take effect; to make impression. r.
      1913 webster

            strong waters pierce metals, and will touch upon
            gold, that will not touch upon silver. --bacon.
      1913 webster

   3. to treat anything in discourse, especially in a slight or
      casual manner; -- often with on or upon.
      1913 webster

            if the antiquaries have touched upon it, they
            immediately
            quitted it.                           --addison.
      1913 webster

   4. naut to be brought, as a sail, so close to the wind that
      its weather leech shakes.
      1913 webster

   to touch and go naut., to touch bottom lightly and
      without damage, as a vessel in motion.

   to touch at, to come or go to, without tarrying; as, the
      ship touched at lisbon.

   to touch on or to touch upon,
      a to come or go to for a short time. r.
          1913 webster

                i made a little voyage round the lake, and
                touched on the several towns that lie on its
                coasts.                           --addison.
          1913 webster
      b to discuss briefly, as only a small part of a
          discourse.
          pjc
see also:
to touch and go to touch at to touch on to touch upon