Tagalog for mountain, borrowed by American soldiers in the Philippines to mean any remote wilderness
From Tagalog 'bundok' meaning mountain. American soldiers stationed in the Philippines during and after the Philippine-American War (1899–1902) adopted the word to describe the rough, mountainous terrain of the Filipino countryside. They brought it back to American English as boondocks, meaning any remote or uncivilized area. The related term boondoggle may also be connected, though that etymology is disputed. Key roots: bundok (Tagalog: "mountain").
U.S. Marines fighting in the Philippine jungles adapted bundok into their slang during the brutal Philippine-American War, which killed over 200,000 Filipino civilians. The word entered mainstream American English decades later through returning WWII veterans who served in the Pacific theater.