We carried out a complete study (magnetic, electronic, dielectric, dynamic, and elastic properties) of the nickel hydroxide [Ni(OH)${}_{2}$] from first-principles calculations based on density functional theory. No theoretical investigations of these physical properties have been previously reported in literature. Our work supports that Ni(OH)${}_{2}$ is an A-type antiferromagnetic material. In addition, it is negative uniaxial and semiconducting with a direct band gap at the $\ensuremath{\Gamma}$ point around 3 eV. By contrast to its electronic dielectric tensor, its static tensor is strongly anisotropic in the plane orthogonal to its optical axis. This anisotropy is mainly governed by a highly polar phonon centered around 510 cm${}^{\ensuremath{-}1}$ and assigned as a rotational ${E}_{u}$ mode. Both Raman and infrared spectra have been computed to clarify the longstanding debate on the assignment of the Ni(OH)${}_{2}$ phonon modes reported in literature. All these theoretical results are fruitfully compared to the experimental ones obtained on large Ni(OH)${}_{2}$ ``pseudosingle'' crystals when available.