We delineate quantum magnetism in the strongly spin-orbit coupled distorted honeycomb lattice antiferromagnet BiYbGeO 5 . Our magnetization and heat capacity measurements reveal that its low-temperature behavior is well described by an effective J eff = 1 2 Kramers doublet of Yb 3+ . The ground state is nonmagnetic with a tiny spin gap. Temperature-dependent magnetic susceptibility, magnetization isotherm, and heat capacity can be modeled well assuming isolated spin dimers with anisotropic exchange interactions J Z 2.6 K and J XY 1.3 K. Heat capacity measurements backed by muon spin relaxation suggest the absence of magnetic long-range order down to at least 80 mK both in zero field and in applied fields. This sets BiYbGeO 5 apart from Yb 2 Si 2 O 7 , with its unusual regime of magnon Bose-Einstein condensation, and suggests negligible interdimer couplings, despite only a weak structural deformation of the honeycomb lattice.