On-premise or on-premises, what will it be?

A colleague recently made me aware of the widely used yet incorrect expression on-premise for software that can be run on a customer’s servers rather than in the cloud. If you look out for it or ask your favourite search engine, you will see just how many people make this mistake. In hindsight, I have to admit that I was probably among them, having heard it so often during presentations.
The upshot is that the correct expression is on-premises. This is actually quite obvious if we consider the very different meaning of the words:
premises: the building and land near to it that a business owns or uses (source: OED)
premise: a statement or an idea that forms the basis for a reasonable line of argument (source: OED)
However, things are somewhat complicated by two minor details:
- premises is always used in its plural form, even if referring to a a single building
- premises is also the plural of premise, so context may be crucial