Another possibility is `index`, which is relatively short and not a
reserved keyword ^1. `position` is not as precise but would avoid the
conceptual overloading of ordinary indices.

I'm not a fan of "index" since that leaves the question of
whether it's 0 or 1 based. "Position" is a bit better, but I think
Jian's suggestion of "occurance" is best.

We do have precedent for one-based `index` in Postgres: array types are
1-indexed by default! "Occurrence" removes that ambiguity but it's long
and easy to misspell (I looked it up after typing it just now and it
_still_ feels off).

How's "instance"?

Presumably someone referencing arguments by name would have just looked up the names via \df or whatever, so presumably misspelling wouldn't be a big issue. But I think "instance" is OK as well.

-- 
Jim Nasby, Data Architect, Austin TX