The beak of the solitaire was slightly hooked, and its neck and legs were long. One observer described it as the size of a swan. The skull was long, flattened at the top with the fore and hind parts elevated into two bony ridges structured with cancellous. A black band (a contemporary description described it as a "frontlet") appeared on its head just behind the base of the beak. The plumage of the Rodrigues solitaire was described as grey and brown. Females were paler than males and had elevations on the lower neck. Sexual size dimorphism in the solitaire is perhaps the greatest in any neognath. One group, probably the males, were considerably larger than the other, measuring in length and weighing up to , whereas the smaller group, probably females, were only and weighed . This is only 60% of the weight of a larger individual. Their weight may have varied substantially due to fat cycles, meaning that individuals were fat during cool seasons, but slim during hot seasons, and may have been as low as in the larger gender and in the smaller. Though male pigeons are usually larger than females, there is no direct evidence for the largest specimens actually being the males of the species, and this has only been assumed based on early works. Though the male was probably largest, this can only be confirmed by molecular sexing techniques, and not skeletal morphology alone.