In summary, we performed density functional theory (DFT) calculations, and predict that the pentagonal boron carbon nitride (p-BCN) monolayer is structurally, dynamically, and mechanically stable direct bandgap semiconductor. The special quasi-sp 3 hybridized B-N and C-N bondings with unique geometry support the monolayer to possess intriguing chemical and physical properties. The biaxial strain creates significant structural reconstruction with shrinking and elongating bond lengths and angles, and thickness. The mechanical response is found very sensitive toward the strain. With the application of a small value of strain, a very rare negative Poisson's ratio (NPR), with hardening to softening, mechanical anisotropy to isotropy is detected. However, the monolayer is mechanically and dynamically unstable at 6% of compression. Additionally, the bandgap is manipulated by loading the biaxial strain. Most importantly, our predictions on p-BCN show excellent optical response such as good static dielectric constant and refractive index, strong optical absorption (up to 1.08×10 5 -1 and 7.01×10 5 -1 in UV) with small energy loss and reflectance peaks both appearing in visible and ultraviolet regions (UV). The anisotropic geometry leads to acquiring strong optical anisotropy behavior in the monolayer. Although the optical response is not very sensitive toward the strain, the blue and red shift, with slight growth/reduction in spectral amplitude is noticed by tailoring with tensile and compressive strain. Hence, these exceptional physical and chemical properties exhibited by the p-BCN monolayer allow it to be a proper candidate material for nanomechanical and optoelectronic device applications.