1776, "dense growth of trees and other tangled vegetation," such as that of the swampy regions at the base of the Himalayas in India, from Hindi jangal "desert, forest, wasteland, uncultivated ground," from Sanskrit jangala-s "arid, sparsely grown with trees," a word of unknown origin.
Extended by 1849 to other places overgrown by vegetation in a wild, tangled mass. Figurative sense "wild, tangled mass" of anything is from 1850. Meaning "place notoriously lawless and violent" is first recorded 1906, from Upton Sinclair's novel. Meaning "hobo camp" is from 1908. Asphalt jungle (1949) is from William R. Burnett's novel title, made into a film 1950 by John Huston; blackboard jungle (1954) is from Evan Hunter's novel title and 1955 movie.
Jungle fever "remittent malignant fever prevalent in India and tropical regions" is from 1803. Jungle gym appears in advertisements from 1921, originally one word, made by Junglegym Inc., Chicago, U.S. Jungle bunny, derogatory for "black person," attested from 1966.