Interdependence of the configurational, vibrational, and anharmonic-force contributions to the entropy of a liquid during its supercooling is investigated, and the effect of the anharmonic-force contribution to the entropy at constant pressure and constant volume conditions is analyzed. For realistic values of the Gruneisen parameter and expansion coefficient of a liquid, this contribution is found to be 30-40% of the heat capacity, which is high enough to affect the relation between the viscosity and excess entropy. An analysis of the resolved contributions to entropy of liquid selenium, an N-type liquid, shows that its configurational entropy is not proportional to its excess entropy.