Due to the presence of lone pair of electron the bond angle decreases
In ethanol the oxygen of $— OH$ group is bonded to the $sp^{3}$ hybridised carbon by a sigma bond. The $—C—O—H$ bond angle in ethanol is less than the tetrahedral angle $(109^{\circ} 28')$ due to larger repulsions between the lone pairs of repulsions between the lone pairs of oxygen. Hence it is $104^{\circ}$ in ethanol
