The word eclair was first used in an 1861 issue of Vanity Fair, when it was borrowed directly from a French word meaning "lightning". It was named that because the dessert was meant to be eaten quickly, and that word comes from Old French esclair, which could be defined as "daylight" or "flash of light". That traces to the Latin verb exclarare, which translates to "illuminate" and was composed of the prefix ex-, meaning "out" (and, as we've seen before, tracing to Proto-Indo-European eghs, also "out") and the root clarus, meaning "clear". Clarus, the etymon of words like declare, clarinet, and Claire, derives from the Proto-Indo-European reconstruction kelh, which meant "call". Since the turn of the century, usage of eclair with an acute accent over the e has been increasing while the variation with no accent has been decreasing. Probably an attempt to make the food seem fancier.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.