[caseymarquis]

Since the word agile has become so loaded, you can instead explain why a waterfall practice is linked to predictable problems and avoid buzzwords entirely:

It takes 6 months to act on customer feedback with our current release strategy, and a full year to fix the bugs related to that feedback. We should be rapidly iterating on feedback quickly to avoid churn. Let's try xyz...

[makeitdouble]

With that approach, the discussion would more look like "Our current cycle takes a full year to complete, let's reduce our projets' scopes by 10 to get down to a month or two at most"

That's even simpler, and you can even keep waterfalling and still benefit from shorter iterations.