A number of experiments have been performed to study magnetic, electronic and optical properties of HoNiSi, along with theoretical calculations. The compound crystallizes in orthorhombic crystal structure and orders antiferromagnetically at TN=4.6 K. Magnetization isotherms show curvature in low fields, revealing a field induced metamagnetic transition. Application of field reduces the resistivity near TN, which results in a large negative MR. The maximum value of MR has been found to be -24% at 4 K for 50 kOe. Strong antiferromagnetic interactions among the moments below 4 K result in positive MR, which changes with field. The antiferromagnetic ordering with the effective magnetic moments of Ho close to the observed value is obtained in the LSDA+U calculations accounting for the electronic correlations in the 4f Ho shell. In the experimental optical conductivity interband transitions involving 4f Ho and 5d Ho forms the main features in good agreement with the theoretical electronic structure of HoNiSi