Cu5SbO6 is found to have a monoclinic, Delafossite-derived structure consisting of alternating layers of O-Cu(I)-O sticks and magnetic layers of Jahn Teller distorted Cu(II)O-6 octahedra in an edge sharing honeycomb arrangement with Sb(V)O-6 octahedra. This yields the structural formula Cu(I)(3)Cu(II)(2)Sb(V)O-6. Variants with ordered and disordered layer stacking are observed, depending on the synthesis conditions. The spin 1/2 Cu2+ ions form dimers in the honeycomb layer. The magnetic susceptibility measured between 5 and 300 K is characteristic of the presence of a singlet-triplet spin gap of 189 K. High resolution synchrotron X-ray diffraction studies indicate that changes in the intra- or interdirner distances between 300 and 20 K, such as might indicate an increase in strength of the Peierls-like distortion through the spin gap temperature, if present, are very small. A comparison to the NaFeO2-type Cu2+ honeycomb compounds Na3Cu2SbO6 and Na2Cu2TeO6 is presented.