Diagnosis of worker among Antkey species. Worker caste monomorphic. Head shape ovoid. Antenna 12-segmented. Antennal club 3-segmented. Antennal scrobe lacking. Antennal insertions at least partly covered by frontal lobes; not surrounded by a raised sharp-edged ridge. Frontal lobes do not obscure face outline between mandible and eye Antennal scapes not conspicuously short; easily extended beyond eye level. Posterolateral corners of head unarmed, without spines. Eyes medium to large (greater than 6 facets); distinctly less than half head length. Mandibles triangular. Mesosoma with erect hairs; shining smooth lacking any areas covered with punctate sculpture. Pronotal spines absent. Propodeum lacking spines or teeth. Waist 2-segmented. Petiole with peduncle; lacking large subpetiolar process. Petiole length greater than petiole height. Postpetiole not swollen, in dorsal view not distinctly broader than long or distinctly wider than petiole. Color shiny dark brown to black.
Among introduced and commonly intercepted Monomorium, M. ebeninum can be distinguished from M. destructor, M. pharaonis and the M. salomonis group by its glassy smooth integument that lacks sculpture even on the mesosoma. Among smooth and shining Monomorium, M. ebeninum is distinguished from M. liliuokalanii by the petiole shape (which is distinctly longer than tall in profile) and from M. floricola by the uniformly dark brown to black color (versus bicolor with dark brown to black head and gaster and paler red or yellow mesosoma, waist and appendages).