Noun, pl. fastigia
1. Apex of the roof of the fourth ventricle of the brain, an angle formed by the anterior and posterior medullary vela extending into the substance of the vermis.
2. The acme or period of full development of a disease.
(Pathology)
3. The most intense phase of a disease (especially a fever). (wiktionary.org)
Word origin: Latin word, top as of a gable; a pointed extremity