Hi... Rant... Ok...?
i think in undertale human would have evolved a broader definition in the sense of vulnerability as in saying "im only human" wouldn't be as associated with human as a species but more with entities of human level consciousness as a whole ,, the term human in the sense of the species may even be outdated/archaic in modern english which is where i propose that human in the sense of one from the homo genus would be replaced mostly or entirely by the word person/people, in which modern humans would be referred to as people and prehistoric people would be referred to as primates. monsters, however, were not there for this gradual shift in language and upon referring to people as "humans" are met with much confusion from non-etymologists who, to their knowledge, are being called "vulnerables" by the monsters. on the topic of monsters, monster as a word may have had an alternative origin (see; prefix monarcho- which would be later shortened to mon from linguistic shifts and suffix -ster) and originally been named that due to their dependence on having a king (or monarch) as seen in every iteration of monsters shown in the game (minus the version of the neutral route where no leader steps up, which can be discluded as if i remember correctly the monsters were hopeless and things got bad shortly after) and the negative connotation of monster came along after people started seeing monsters as lower class citizens and lesser than people, and after monsters were no more than a legend, it gained the definition of a beast or otherworldly bad creature, combined with the coinciding rising of the latin root of the word monster (monere to monstrum to monstre to monster,) gave the word monster its negative connotation overall. on the note of monsters being lower class citizens, several slurs were likely used to refer to monsters considering the selfish and defensive and fearing-of-all-things-different-than-them-which-manifests-as-discrimination nature of humans. some potentials i thought of were 1. Strayface, used in reference to monsters that resemble anthropomorphic animals, comes from stray (animal) + face, pretty much saying you have the face of a stray animal and the body of a person. 2. Tykeblood, also used of animal-like monsters, comes from tyke (mongrel/mixed-breed) + blood. and 3. Hexheart, used towards monsters in general, originates of hex (magical curse) + heart (in reference to their souls) since their souls and bodies are made of magic and a bad kind of magic would be a hex, it's like calling someone bad-natured and evil because their body and soul is made of magic.