[1] I oppose the death penalty as it is used today. Making an example of psycho serial murderers is pointless, because it's not like that conduct can be deterred.

Original intent is historically how the constitution has been been interpreted by courts, at least once ambiguity in the plaintext has been found.

Original meaning is a modern approach propounded most famously by Justice Scalia.

The difference is that original meaning focuses on the definition of words and phrases as understood at the time of drafting or ratification, and in the relevant context in which they're used, regardless of intent or purpose. It's like an abstract version of plaintext but which is supposed to overcome (with a suitable amount of handwaving) the deficiencies of a plaintext, literalist approach. Original intent, by contrast, focuses on what the drafters or legislatures thought the law would accomplish. The literal meaning and the original meaning are both strong evidence and often dispositive, but they're hardly exclusive.

Original meaning is supposed to be a more concrete examination, less susceptible to contemporary political prejudices and likely to be more consistent over time. But I think in actuality that has proven false. Language is far more flexible than Scalia and similarly-minded jurists believe. Lawmakers regularly write statutes that either rely on judicial precedent, or that put the onus on courts to decide material issues, especially when ambiguity and plausible deniability is politically expedient. Certainly there are indisputable examples of this in the constitution. For these and many more reasons, the functions of a judge simply cannot be reduced to such mechanical approaches. And they probably shouldn't be.

Many of the drafters of the constitution were lawyers. Most were versed, more or less, in the common law. The drafters used common law phrases; many of which had _already_ undergone an evolution in their meaning and application; many of which were de novo inventions of English courts altogether. They clearly used ambiguity to their advantage when reaching consensus on clearer language was difficult or inconvenient. So we'd be naive to think that their view of the common law was of a static, unchanging approach, or that they didn't expect courts to take license.

Scalia would probably admit much of that. (He certainly admitted some of that in his many essays on the subject.) But in his view even if the drafters wanted courts to use traditional approaches to statutory interpretation, that's been a failed experiment. In his view, preservation of the higher ideals of the constitution, like separation of powers and democracy, demand that courts use original meaning, even if it subverts original intent in the particular.

I disagree with Scalia roundly. But whether you agree or disagree or fall somewhere in the middle, the fact of the matter is that original meaning is a very modern approach. By contrast, only extreme proponents of thea "living constitution" can be considered wholly modern; in some understandings "living constitution" is just a recognition and embrace of the reality of constitutional interpretation and application. Scalia's application of original meaning changed so much over the decades that he's a prime example of the inherently dynamic nature of the business and the rules it produces.

Nonetheless, I suppose we could say that his arguments have effectively shifted the "Overton window". Scalia managed to convince even ardent liberals like Ginsburg that traditional approaches to constitutional interpretation used during the 18th, 19th, and much of the 20th centuries were inappropriate. That there was a need to "return to the text", as-if courts somehow had ever ceased doing that. Scalia often made unfounded or poorly researched historical claims, and most jurists have already internalized much of it. Scalia is hardly unique in having that effect; I spent half of law school using Google Scholar and other historical databases disproving various historical claims in legal decisions and treatises. Most people don't even realize that there were multiple transcriptions of old decisions, and sometimes they conflicted. Which one was put into a legal treatise was sometimes the real inflection point in the law, not the legal opinion itself.

But his effect is unique, I think, in shifting the entire judiciary to the right. Usually such things are a mixed bag from a political perspective.