1868, adj. and noun, as a racial designation, literally "resembling the Mongols," from Mongol + -oid. Compare Mongolian. In reference to the genetic defect causing mental retardation (mongolism), by 1899, from the typical facial appearance of those who have it. See Down's Syndrome. Such people were called Mongolian from 1866.
Entries linking to mongoloid
Mongol
1738 (n.) "one of a people of Mongolia and adjacent regions;" 1763 (adj.), from a native name, said to be from mong "brave." Related: Mongolia.
-oid
word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeidēs (three syllables), from eidos "form," related to idein "to see," eidenai "to know;" literally "to see" (from PIE *weid-es-, from root *weid- "to see"). The -o- is connective or a stem vowel from the previous element. Often implying an incomplete or imperfect resemblance to the thing indicated.