1520s, "a sensation of taste, a flavor distinctive of anything," alteration of reles "scent, taste, aftertaste," (c. 1300), from Old French relais, reles, "something remaining, that which is left behind," from relaisser "to leave behind," from Latin relaxare "loosen, stretch out," from re- "back" (see re-) + laxare "loosen" (from PIE root *sleg- "be slack, be languid").
Especially "a pleasing taste," hence "pleasing quality" in general. The meaning "enjoyment of the taste or flavor of something" is attested from 1640s. The sense of "condiment, that which is used to impart a flavor to plain food to increase the pleasure of eating it" is recorded by 1797, especially a piquant sauce or pickle: The modern stuff you put on hot dogs (or don't) is a sweet green pickle relish.
updated on June 25, 2021