Eureka (word)
The exclamation 'Eureka!' is attributed to the ancient Greek scholar Archimedes. He reportedly proclaimed "Eureka! Eureka!" after he had stepped into a bath and noticed that the water level rose, whereupon he suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged. (This relation is "not" what is known as Archimedes' principle—that deals with the "upthrust" experienced by a body immersed in a fluid.) He then realized that the volume of irregular objects could be measured with precision, a previously intractable problem. He is said to have been so eager to share his discovery that he leapt out of his bathtub and ran naked through the streets of Syracuse.
Aranyaka
Several theories have been proposed on the origin of the word "Aranyaka". Originally, as per Oldenberg (1915), it meant (dangerous texts to be studied in the wilderness (Taitt. Ar. II). A later, post-Vedic theory holds that these texts were meant to be studied in a forest, while the other holds that the name came from these being the manuals of allegorical interpretation of sacrifices, for those in Vanaprastha (retired, forest-dwelling) stage of their life, however the Vanaprastha Ashrama came into existence only well after that of the Sanyasin (Sprockhoff 1976) -- according to the historic age-based Ashrama system of human life.