vicinal

Adjective

vicinal (not comparable)

1. Of or pertaining to a neighborhood; neighboring.
2. Describing identical atoms or groups attached to nearby (especially adjacent) atoms in a molecule.
   • In spite of the analogy of dative bonds with covalent bonds in that both types imply sharing a common electron pair between two vicinal atoms, the former are distinguished by their significant polarity, lesser strength, and greater length.1999 October 30, IUPAC, “Glossary of terms used in theoretical organic chemistry (IUPAC Recommendations 1999)”, in Pure and Applied Chemistry, →DOI, page 1933
3. Describing subordinate planes on a crystal, which are very near to the fundamental planes in angles, and sometimes take their place.