a. [ L. vicinalis: cf. F. vicinal. ] 1. Near; vicine. T. Warton. [ 1913 Webster ]

2. (Organic Chem.) Having the substituted groups on the same carbon atom. [ PJC ]

Vicinal planes (Min.), subordinate planes on a crystal, which are very near to the fundamental planes in angles, and sometimes take their place. They have in general very complex symbols. [ 1913 Webster ]