The Collaborative International Dictionary of English v.0.48:

Heliac \He"li*ac\, a.
   Heliacal.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heliac
    adj 1: pertaining to or near the sun; especially the first
           rising of a star after and last setting before its
           invisibility owing to its conjunction with the sun; "the
           heliacal rising of the Dog Star"; "the heliacal or Sothic
           year is determined by the heliacal rising of Sothis (the
           Egyptian name for the Dog Star)" [syn: heliacal,
           heliac]