I flew to the medical dictionaries for elucidation on this word, which formally refers to a person having an abnormally long and narrow skull, misshapen due to a congenital condition. What happens is that one or more of the sutures in the head — fibrous joints between the bones of the skull — close before the brain has finished growing.
The condition is recorded under many different names, depending on which sutures are involved and the shape of the resulting deformation; some of the other terms are acrocephaly (Greek akron, tip), dolichocephaly (Greek dolikos, long), plagiocephaly (Greek plagios, slanting), brachycephaly (Greek brakus, short), trigonocephaly (Greek trigonos, three-cornered), tectocephaly (Latin tectum, a roof), oxycephaly (Greek oxus, sharp), and scaphocephaly (Greek skaphos, a light boat or skiff).
In all these terms, the last element is from Greek kephale, head. In cymbocephalic the first part is from another Greek word for a small boat, kymbe.