Difference in usage between the nouns "merge" and "merger"

As a non-native speaker I am having some trouble distinguishing between the two words "merge" and "merger". To me, it sounds like "merger" describes a major event, often occurring between legal entities such as companies, countries, pieces of industry,... In computer science, I have more often seen merge used as a noun, e.g. if in a version control system two branches are merged, the result is called a merge. The process while it is occurring is also called a merge.

Are the two terms interchangeable, or are there clear distinctions in usage (in general practice)?

In everyday use, merge is not used as a noun. You can see this in the following Google ngrams

Oxford dictionaries, Merriam Webster and dictionary.com have yet to record it as a noun, if they ever will. As far as I'm aware merge is only used as a noun in the context of source control.

However, as Barrie points out, the OED does list merge as a noun that means

an act or instance of merging; a merger.

So it seems that merge is used in this way outside of source control.

I have also found 1 hit in COCA for merge as a noun, although that looks like a mistake. I couldn't find any hits at the BNC.

I think if you use merge to mean merger, outside of source control, you will be understood, but it isn't widely done.