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Douglas Harper's Etymology Dictionary
Sino-

before vowels Sin-, word-forming element meaning "Chinese," 1879, from Late Latin Sinæ (plural) "the Chinese," from Ptolemaic Greek Sinai, from Arabic Sin "China," probably from Chinese Ch'in, name of the fourth dynasty of China (see China).

Wiktionary
sino-

pre. 1 A combining form of sinus. 2 (alternative case form of Sino- English)