Brian H wrote:

…Sustainable means that – sustainable. Capable of feeding the world, on a sustainable basis.

No, it doesn’t. It pre-defines “sustainable” to equate to some partimular model of agriculture, life-style, etc., with zero comprehension of technology and what the know and unknown alternatives might be. It’s a “freeze in place” code-word, with the place designed by the speaker.

Partimular, you say?

Interesting use of pronouns. “no, it doesn’t” – “it” refers to “sustainable means…”
Then, “It predefines…” – what is “it” there?

I suspect the second “it” would be “some folks”. Well, OK, some folks do. I have come across people who want to freeze some idealized life-style in place, but they aren’t ALL folks, and certainly, they don’t have exclusive rights to the word.

I likewise used to think of “sustain” as limiting – keeping everything the same. I thought it meant “unchanging, forever”. Which I found unsatisfying, because I am comfortable with a dynamic model of the environment, and was actually hoping to “improve” the environment, as measured by increasing habitats, lushness, biodiversity, etc. “sustain” to me meant, this is as good as it gets, let’s not lose any more ground, zero sum with human population and resource use.

But it doesn’t really mean that. You don’t need to limit yourself to that. You don’t need to pretend that others are limiting themselves.

Of course, you don’t need to pile all that onto the poor word. It has a simple job, just addressing resilience and continuity. From a dictionary:

sustain |səˈstān|
verb [ trans. ]
1 strengthen or support physically or mentally : this thought had sustained him throughout the years | [as adj. ] ( sustaining) a sustaining breakfast of bacon and eggs.
• cause to continue or be prolonged for an extended period or without interruption : he cannot sustain a normal conversation | [as adj. ] ( sustained) several years of sustained economic growth.
• bear (the weight of an object) without breaking or falling : he sagged against her so that she could barely sustain his weight | figurative his health will no longer enable him to sustain the heavy burdens of office.
2 undergo or suffer (something unpleasant, esp. an injury) : he died after sustaining severe head injuries.
3 uphold, affirm, or confirm the justice or validity of : the allegations of discrimination were sustained.