"Block" and "function" already have pretty well defined meanings to
software engineers; I don't think that re-using the terms but changing
the definitions makes a whole lot of sense in the context of a new
programming language (the engineering definition of "function" is
basically the same as "subroutine," which is sad because "function"
would actually fit pretty well if it didn't have all the baggage).

I would personally prefer to learn a "new" term (in the sense that
morphism isn't commonly used when discussing programming languages)
that is well defined in the context of the language in question than
to have to try and override years of habit when it comes to thinking
about what a "block" or "function" is.  If the term has a
well-established meaning in other fields that maps very closely to the
language construct, all the better.

If it doesn't map closely, though, I think that nelogism makes more
sense than trying to commandeer a term already in use.

If we're going for overly clever, I'd like to suggest "rill", as it's
the basically the smallest channel through which water naturally
flows.  ;)

Eli