[Tortured title fixed]
I have taken to objecting to linguistic torture rather emphatically and frequently. I really ought to clarify.
If people use the word: "Happiness" to mean something relatively (but not completely) specific, then any use of happiness that violates that standard general shared meaning is rhetorical cheating and bad philosophical practice.
Happiness -- Everyone agrees that happiness is: a specific (set of) emotion(s)...alternately a sense of life-satisfaction.
People do research on the topic of happiness. People from Aristotle to Buddha to Lao Tzu to Will Willkinson write on the topic of happiness...and in a very rough sense, it's pretty clear that we're all talking about the same thing (or as I believe, set of things).
Happiness is well understood to be something that we get when we get the girl...and something that we don't get when we get beaten up.
If you try to use the word "happiness" to mean anything we pursue (the theory we all pursue happiness)...we are no longer talking about happiness. We are talking about some other idea: "Squibblix: That which we all pursue". If you are talking about happiness instead of Squibblix, it's because you want some or all of the value of the word happiness to rub off on your concept of squibblix. If you don't want to steal some of the value of the happiness word without justifying your theft...you should stick with nonsense words so no one gets confused and thinks you're using stuff in an English sense. Unless, of course, you are deliberately trying to confuse people....in which case I suggest you stop.
Other words that suffer from this problem:
Randian "Selfishness" -- I did this badly myself for a solid 5-7 years...and since I have become extra-sensitive to bad word-usage which leads to uncareful thinking.
In normal English, "selfishness" includes active disregard for others' preferences.
The words "self-interest" or "prudence" is the word used by english-speaking people in order to indicate behaving basically smartly.
"Self-interest" and sometimes "selfishness" also are frequently cheated aroudn a different way.
What is the purpose of the word "self-interested"?
To distinguish between acts that are morally praiseworthy like helping your team, and acts that are not morally praiseworthy like helping yourself. The purpose of the word is to draw a useful distinction that applies to lots of life. And the word is useful in that context. If you try to use the word "self-interested" to explain a normal (non machiavellian) person's basic kindness...you're torturing the word. The existence of the term is in order to distinguish between two classes of acts...and you're now using the word to describe both sides of the divide? It's like stretching the word on the metaphorical rack. Status games around your ability to confuse intellectual opponents? Or just confusion as to the purpose of the word?
Libertarian -- Libertarian is a word used by an awful lot of folks to mean any of several dozen varieties of folks who want *a lot* less government. It's a very common political label, and could be assigned to folks with lots of different approaches. The key is: radical decrease in quantity of government, radical increase in amount of freedom. Folks who claim: Bob is not a libertarian because he hasn't signed the non-initiation of force maxim have lost the battle for the word.
Christian -- I used to, in college, hang with a bunch of evangelicals who claimed that Catholics weren't Christians. Others say the same thing about Mormons. While this term is subject to dispute....it's almost universally accepted as meaning something like: someone inside the Abrahamic tradition who accepts the divinity of Christ, and rejects the prophet-ness of Mohammed. Catholics, Mormons, Evangelicals, etc.
What am I missing?
Use words how they're used in English. If you try to change the meaning of words...it just confuses the conversation. Far better, outside of surreptitious persuasive context, to use a made-up word than to redefine an existing, and nearby word.