venture — an undertaking involving uncertainty as to the outcome, especially a risky or dangerous one: a mountain-climbing venture.
Three-syllable rhymes
adventure — If someone has an adventure, they become involved in an unusual, exciting, and rather dangerous journey or series of events.
debenture — A debenture is a type of savings bond which offers a fixed rate of interest over a long period. Debentures are usually issued by a company or a government agency.
indenture — a deed or agreement executed in two or more copies with edges correspondingly indented as a means of identification.
Four-or-more syllable rhymes
misadventure — an instance of bad fortune; mishap.