I prefer to have a kitchen-cum-living room if possible.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means concurrently, but since you can't "to concurrently", we're going to have to come up with another word to use: "to combine" or "to double as." Since this kanji has to do with something having a dual purpose, we can say that something can combine as being another thing, or double as being another thing, which is where these words come from.
For example, a car (か) can double as a place to sleep at night when not enough people become members of WaniKani.