D defs.my
Entry 2 senses Webster, 1913

Vicinal

· Vic·i·nal · IPA /ˈvɪsɪnəl/
01 a. Near; vicine.
  1. 1.
    Near; vicine.
  2. 2.
    Having the substituted groups on the same carbon atom.(Organic Chem.)
Phrases & compounds
Vicinal planes — 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.