1748 (in Chesterfield's "Letters"), but rare before c.1800 as an Eng. institution, from Fr. piquenique
(1692), perhaps a reduplication of piquer
"to pick, peck," from O.Fr. (see pike
(2)), or the second element may be nique
"worthless thing," from a Gmc. source. Originally a fashionable pot-luck social affair, not necessarily out of doors. Figurative sense of "something easy" is from 1886.