The side opposite an angle is the side that does not form part of the angle. Side $\displaystyle{\overline{{{B}{C}}}}\usepackage{cmbright}\Huge\$ is a side of $\displaystyle\angle{C}\usepackage{cmbright}\Huge\$ . Side $\displaystyle{\overline{{{B}{C}}}}\usepackage{cmbright}\Huge\$ would be the adjacent side for $\displaystyle\angle{C}\usepackage{cmbright}\Huge\$ .