"a widow," mid-15c., relicte, etymologically "one who is left, one who remains," from Old French relict, fem. relicte, "person or thing left behind" (especially a widow) and directly from Medieval Latin relicta "a widow," noun use of fem. of relictus "abandoned, left behind," past-participle adjective from Latin relinquere "leave behind, forsake, abandon, give up," from re- "back" (see re-) + linquere "to leave" (from PIE *linkw-, nasalized form of root *leikw- "to leave").
In later only a semi-legal or formal term (perhaps from confusion with relic), "more often seen than heard" [Fowler]. Also as an adjective in Middle English and early modern English, originally "left undisturbed or untouched, allowed to remain" (mid-15c.) but used in various senses.