[jdmichal]

But people also write:

    for(int i = 1; i <= n; ++i)
        sum += i;

This would look immediately wrong if i was actually index.

Also, your analogy to linguistic concepts is bad. Sure I call people Bob, but I'm also not expecting to have to reread my conversation with them half a year later and modify it to say something else instead. Also, those linguistic concepts are not idioms. They are just alternate names and indexical constructions, respectively. An idiom is something like "What's up?", where the literal meaning of "what is up" is not intended, but rather another meaning that is completely lost unless you are in the know.