Definition of: vicinal

(vis′ə·nəl) adjective
1. Neighboring; adjoining; near.
2. Mineral. Designating a crystal form closely approximating one of the fundamental forms.
3. Chem. Designating a benzene derivative in which the substituted elements or radicals are in consecutive order on the benzene ring. [<L vicinalis <vicinus a neighbor, orig. nearby]