Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English sweart "black," from Proto-Germanic *swartaz (cf. Old Frisian and Middle Dutch swart, Old Norse svartr, German schwarz, Gothic swarts "dark-colored, black"), from PIE root *swordo- "dirty, dark, black" (source of sordid). The true Germanic word for "black," surviving in the Continental languages.