Horton-Smith dates merenda, an afternoon meal to the Fifth Century BCE. He believes it is derived from mereo, another Latin word that suggests sharing.
As the word evolved, the Italians use merenda and the Spanish as merienda
It’s a stretch to link merenda with the French word piquenique, the words are so disparate. But the idea of sharing is an important element of is common to all, and central to Gilles Ménage’s 1964 Parisian dinning style.
See Lionel Horton-Smith. “Further Notes on the Origin of the Gerund and Gerundive,” The American Journal of Philology, Vol. 16, No. 2 (1895), pp. 217-222]