Early 18th century; earliest use found in John Moyle (d. 1714), naval surgeon. From classical Latin aestuōsus excessively hot, sweltering, having a high bodily temperature, (of water) seething, raging from aestus heat, hot weather, hot season, summer, high bodily temperature, feverishness, fire of love, passion, rage, fury, spray, rough sea, surge, ebb and flow, tide, flood, current, commotion, tumult, mental disturbance, worry + -ōsus. Compare Middle French aestueux boiling, French (rare) estueux burning.