Learn English – What were sideburns called before the Civil War

One possibility could be "wodan dreame".

Before getting to this point I'd like to add that whereas the spelling "nightmare" is indeed recent (see the corresponding Google ngram), more archaic spellings are reported in the OED; viz "niȝt-mare" (1290), "nytmare" (1340) and "Nyghte Mare" (1440).

Leaving aside older spelling of "nightmare", I also came across an article on Google books suggesting that when preceded by "wod" or "wodan", then the dream turned out to be a nightmare...

This is in line with Wodan's main domains of death, war and afterlife. The article oldest quote is circa 890 and there are also quotes from Ælfric of Eynsham. Unfortunately the pages after 161 are not available from Google books.

Update
Then, starting with the 18th century the Latin world "incubus" was in use. But that's not Old English any more I'm afraid. It's still used in Italian (under the form incubo) actually.

The Online Etymology Dictionary says sustainability is from 1972, though its root words are much older.

sustainable
1610s, "bearable," from sustain + -able. Attested from 1845 in the sense "defensible;" from 1965 with the meaning "capable of being continued at a certain level." Sustainable growth is recorded from 1965. Related: Sustainability (1972).

An article by Nathan Thanki called Sustainable: a philological investigation gives some background, here's an excerpt that neatly links sustainability with Nachhaltigkeit:

So it is what we are trying to sustain that is usually the meat of arguments about “sustainability”—is it overconsumption, overpopulation, environmental degradation? The term has become synonymous with that “meat” in the past few decades. The Club of Rome, in its 1972 report, “Limits to Growth,” claimed that it was searching for a global equilibrium, “a world system that is: 1. sustainable without sudden and uncontrolled collapse; and 2. capable of satisfying the basic material requirements of all of its people.” When the World Commission on Environment and Development (aka the Brundtland Commission) concluded with the notion of “sustainable development,” the emergence of the concept we know too well today was fully underway. Since that time, sustainability has come to be almost synonymous with “sustainable development, defined in Our Common Future as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”
...
While the origins of the words association with the environmental seem to lie in the emergence of the environmental movement of the 70s, Ulrich Grober points out a deeper root. In “A conceptual history of ‘sustainable development’ (Nachhaltigkeit),” he argues that the term actually comes from 18th Century forestry (at the time timber was a key resource with an uncertain future). German nobleman and forester Hans Carl von Carlowitz wrote “’daß es eine continuirliche beständige und nachhal–tende Nutzung gebe,’ (that there would be a continuous, steady and sustained use).” Sadly, Europe no longer has any primeval forest outside of the Białowieża Forest in Poland and Belarus.So it would appear to me that the quest for “sustainability” is older than we commonly recognise, and, thus, so is our failure to achieve it: marking the failure of civilization.

Edit: The 1972 date is surprisingly late, here are some antecedents from 1906 and 1907.