hyperfine structure: Meaning and Definition of

hy'per•fine' struc'ture

Pronunciation: (hī'pur-fīn', hī"-), [key]
— Physics. Physics.
  1. the splitting of the lines of an atomic spectrum, produced by the angular momentum of the nucleus of the atom. Cf. fine structure.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.