[ adj ] belonging to or limited to a vicinity <adj.pert>
Vicinal \Vic"i*nal\ (?; 277), a. [L. vicinalis: cf. F. vicinal.] 1. Near; vicine. --T. Warton.
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.