Eureka (word)
"Eureka" comes from the Ancient Greek word "heúrēka", meaning "I found (it)", which is the first person singular perfect indicative active of the verb "heuriskō" "I find". It is closely related to heuristic, which refers to experience-based techniques for problem solving, learning, and discovery.
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.