Originally Posted by Atmas

1. Used in indicating a thing with two roles, functions, or natures, or a thing that has changed from one to another.

He built a bus-cum-greenhouse (= he converted a bus to a greenhouse) that made a bold statement, but the plants in it didn't live very long.

* p. 1926, a. 1950, George Bernard Shaw, Collected Letters: 1926-1950,[1] University of California/Viking (1985), page 31,

He is too good an actor to need that sort of tomfoolery: the effect will be far better if he is a credible mining camp elder-cum-publican.

2.Used in English place names to indicate a combined parish that functions as a single unit.

Chorlton-cum-Hardy