I have been looking at the interpretation of the word "for" in the phrases "for example" and "for instance", but I cannot make sense of it. The Oxford Dictionary lists 12 uses of "for" as a preposition, but to me, the "for" in the aforementioned phrases do not seem to match any of them.
Are these phrases some type of exceptions, where we can only interpret them jointly? In other words, is the "for" in these phrases not literally acting as a "for" preposition? Is this perhaps a phrase which came up as a simplification of what could be a literal yet longer alternative, like in
I am a keen reader. To give you an example of this, last week alone I read fourteen books.