"niggard: 1366, nygart, of uncertain origin. The suffix suggests Fr. origin (cf. dastard), but the root word is probably related to O.N. hnøggr "stingy," from P.Gmc. *khnauwjaz (cf. Swed. njugg "close, careful," Ger. genau "precise, exact"), and to O.E. hneaw "stingy, niggardly," which did not survive in M.E.
nigger: 1786, earlier neger (1568, Scot. and northern England dialect), from Fr. nègre, from Sp. negro (see Negro). From the earliest usage it was "the term that carries with it all the obloquy and contempt and rejection which whites have inflicted on blacks" [cited in Gowers, 1965]..."
If I recall correctly, there was a case of a teacher at a US university being sacked for using the word niggardly in a speech, which his employer took to be a racist epiphet. I don't know what finally happened.