Source : Webster's Revised Unabridged Dictionary (1913)

Perihelion \Per`i*hel"ion\, Perihelium \Per`i*he"li*um\, n.; pl.
   {Perihelia}. [NL., fr. Gr. ? about, near + ? the sun.]
   (Astron.)
   That point of the orbit of a planet or comet which is nearest
   to the sun; -- opposed to {aphelion}.

Source : WordNet®

perihelion
     n : periapsis in solar orbit; the point in the orbit of a planet
         or comet where it is nearest to the sun [ant: {aphelion}]
     [also: {perihelia} (pl)]