Source : Webster's Revised Unabridged Dictionary (1913)

Equatorial \E`qua*to"ri*al\, a. [Cf. F. ['e]quatorial.]
   Of or pertaining to the equator; as, equatorial climates;
   also, pertaining to an equatorial instrument.

Equatorial \E`qua*to"ri*al\, n. (Astron.)
   An instrument consisting of a telescope so mounted as to have
   two axes of motion at right angles to each other, one of them
   parallel to the axis of the earth, and each carrying a
   graduated circle, the one for measuring declination, and the
   other right ascension, or the hour angle, so that the
   telescope may be directed, even in the daytime, to any star
   or other object whose right ascension and declination are
   known. The motion in right ascension is sometimes
   communicated by clockwork, so as to keep the object
   constantly in the field of the telescope. Called also an
   {equatorial telescope}.

   Note: The term equatorial, or equatorial instrument, is
         sometimes applied to any astronomical instrument which
         has its principal axis of rotation parallel to the axis
         of the earth.

Source : WordNet®

equatorial
     adj 1: of or relating to or at an equator; "equatorial diameter"
     2: of or relating to conditions at the geographical equator;
        "equatorial heat"
     3: of or existing at or near the geographic equator;
        "equatorial Africa" [ant: {polar}]