"member of a black-skinned race of Africa," 1555, from Sp. or Port. negro "black," from L. nigrum (nom. niger) "black," of unknown origin. Use with a capital N- became general early 20c. (e.g. 1930 in "New York Times" stylebook) in ref. to U.S. citizens of African descent, but because of its perceived association with white-imposed attitudes and roles the word was ousted late 1960s in this sense by Black (q.v.).
Negress (1786) is from Fr. négresse, fem. of nègre "negro." Negroid is attested from 1859, a hybrid, with Gk. suffix -oeides "like, resembling."
"Professor Booker T. Washington, being politely interrogated ... as to whether negroes ought to be called 'negroes' or 'members of the colored race' has replied that it has long been his own practice to write and speak of members of his race as negroes, and when using the term 'negro' as a race designation to employ the capital 'N' " "Harper's Weekly," June 2, 1906