The more the medium, the slower a transverse wave propagates.

Transverse wave is the form of wave in which particles of medium vibrates about their mean position perpendicular to the direction of motion of wave. The transverse wave propagates with slow speed in denser medium because the particles of a much more dense materials has the characteristic of less space between the molecular structure of the material, this requires multiple and combination of movement or vibration between this materials to propagate the wave.