Semimonocoque
The term Semimonocoque is a relatively new variation on the general concept of a stressed skin structure and has mutated over time as the English language sometimes tends to. This explains why references to the term semi-monocoque can only be traced back to around 1980's. If one was to assume that a monocoque structure is one where the skin takes 'most' of the load then introducing a semi version makes no real sense. Take for example a stressed skin structure of a modern aircraft.[1] would the skin stay in its profile and remain being able to carry the stressed load without a sub structure. Highly unlikely. Would an aircraft fly with just the substructure and no outside skin. Extremely unlikely. Therefore for any structure that isn't a perfect egg shell to self-support its skin to carry its own load, the skin needs a substructure to retain and control form. This is true for aircraft, railway carriages and any over device that is...stressed skin. Therefore breaking the monocoque term in monocoque and semi monocoque is a language based utilization rather than a logic extension of the original term monocoque.
Overview
The use of the term semimonocoque when trying to explain semi stressed skin structures has taken the use of the original word monocoque beyond its original intent.
Combination construction
Some aircraft use a combination of construction methods. The Mooney range of four seat aircraft, for instance, use a steel tube truss frame around the passenger compartment with monocoque behind.