Here, in this report, saponin-capped triangular silver nanocrystals have been synthesized in aqueous system by using only Trigonella foenum-graecum seed extract as a reducing agent. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and atomic force microscope (AFM) have been used for the study of their morphological and structural characterization, which indicate that the synthesized nanoparticles are crystalline in nature with triangular morphology having the edge length of the triangle as 80 nm approximately. UV/Vis study of the nanoparticle solution shows three absorption peaks at wavelength of 360 nm, 432 nm, and 702 nm, and these are respectively related to the transverse and longitudinal oscillations of electron, which remain almost in the same position for more than 6 months, indicating the formation of silver nanocrystals with a higher stability. Further, Fourier transform infrared spectroscopy (FTIR) spectra clearly indicate the capping of nanoparticles by saponin, one of the components of Trigonella foenum-graecum extract.