bigheaded

noun

1. Informal. an excessive estimate of one’s importance; conceit.
2. Veterinary Pathology.
   1. an inflammatory swelling of the tissues of the head of sheep, caused by the anaerobic bacillus Clostridium novyi.
   2. enlargement of the head and jawbones of horses resulting from nutritional hyperthyroidism.

noun

1. informal a conceited person
2. US and Canadian informal conceit; egotism
3. vet science
   1. an abnormal bulging or increase in the size of an animal’s skull, as from osteomalacia
   2. any of various diseases of sheep characterized by swelling of the head, esp any caused by infection with Clostridium bacteria