The crossword solution for the term 'Thoreau Subject' is 'POND'. Henry David Thoreau was an American author, poet, philosopher, and naturalist who lived in the mid-1800s. He is best known for his book Walden, which details his two-year experience living in a cabin near Walden POND in Massachusetts. Thoreau's writings often focused on nature and the environment, and Walden POND was a major source of inspiration for him.