also aestivate, "to spend the summer," 1620s, from Latin aestivatus, past participle of aestivare "reside during the summer" from aestus "heat," aestas "summer," literally "the hot season," from Proto-Italic *aissat-, from PIE *eidh- "to burn" (see edifice). Related: Estivated; estivating; estivation.