swarthy: [16] Old English sweart meant ‘black’. It came from a prehistoric Germanic *swartaz, which also produced German schwarz, Dutch zwart, Swedish svart, and Danish sort, and may go back ultimately to the same Indo-European base as gave Latin sordidus ‘dirty’ (source of English sordid [16]). It survives, just, in modern English as swart ‘dark, black’. From this in the 16th century was derived the now defunct swarty, of which swarthy is an unexplained variant. => sordid
swarthy (adj.)
"dark-colored," especially of skin, 1580s, unexplained alteration of swarty (1570s), from swart + -y (2). Related: Swarthiness.