But it’s based on a misunderstanding. Xenomorph just means “alien”— it wouldn’t make any sense for that to be the term for that specific alien, because their existence isn’t common knowledge.
In "Aliens", when Hudson (or was it Hicks?) asks, "is this another bug hunt?" the lieutenant says, (paraphrasing) "there may be a xenomorph involved".
I interpret this to mean that
(a) The marines have previously fought alien creatures of some kind (and they had no problem dealing with them).
(b) They used the term "xenomorph" to mean any alien creature--not specifically the titular alien, which they had never before encountered.
So I agree. Calling it "the Xenomorph" is a misunderstanding. At best it's like calling something "the Beast", or calling all ships of a certain size "dreadnoughts".
The Marines also referenced sexual relations with "Arcturians" which might be human colonists or sentient aliens.
I really like your point about the Marines having fought/hunted/exterminated other "bugs". It casts their bravado in a different light. Even after seeing catastrophic damage from "acid for blood", the Marines are still very confident, which after beating other alien species, makes perfect sense. It's only when they get into the nest do they start getting scared.
I love the scene where the marines go in for the first time. They start out well-disciplined, well-trained badass marines, but things start to go wrong one by one. First, they have to put away their rifles (too close to the fusion reactor), then they see movement on the motion-detector but can't see anything ("Maybe they don't show up in infrared"). Once Apone gets killed, the entire unit falls apart. They come out shell-shocked and demoralized.
It's just an adjective. It would literally be like calling your aliens "humanoids". It describes a shape, literally "alien-shaped", probably because all the other animal-shape adjectives were inadequate.
It isn't a portmanteau, it's a classic Greek word construction (an ordinary expression of classic Greek morphology). "Morph" generally just means "shape" as a Greek root so "xenomorph" is more accurately "alien-shaped". Which gets back to it being a very generic term said in a fancy way (like "we don't even know if it is an alien, we just know it is alien-shaped"), like much technical and scientific jargon will do when it goes to constructing Greek words to describe something ("gynomorph" => "woman-shaped"; to call to a different sci-fi horror Species).
