The Collaborative International Dictionary of English v.0.48:

Perihelion \Per`i*hel"ion\, Perihelium \Per`i*he"li*um\, n.; pl.
   Perihelia. [NL., fr. Gr. peri` about, near + "h`lios the
   sun.] (Astron.)
   That point of the orbit of a planet or comet which is nearest
   to the sun; -- opposed to aphelion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

perihelion
    n 1: periapsis in solar orbit; the point in the orbit of a
         planet or comet where it is nearest to the sun [ant:
         aphelion]