fine structure 
(fīn)
(fīn)n.
1. Physics The splitting of atomic spectral lines into closely spaced groups around a single wavelength, caused by the magnetic moments of orbiting electrons in the nuclei.
2. Biology See ultrastructure.
- improper
- improper fraction
- improper integral
- improperly
- improperness
- impropriety
- improv
- improvable
- improvably
- improve
- improvement
- improvidence
- improvident
- improvidently
- improvisation
- improvisational
- improvisationally
- improvisator
- improvisatorial
- improvisatory
- improvise
- improviser
- improvisor
- imprudence
- imprudent