From Sinae + -ic, q.v., under influence of Judaic, Altaic, etc. and French sinique.
Meanings
(obsolete, rare) Synonym of East Asian, with especial focus on Chinese people and culture: of or related to the Sinosphere.
We will separate [the 'Yellow Race'] into three branches—the Hyperborean, the Mongolian, and the Sinaic branches. 1872, Guillaume Louis Figuier, The Human Race, page 205: