Well let me remind you:
"Married, engaged, or otherwise romantically paired." According to Merriam-Webster what is at play is a sexual relationship or a pre-sexual relationship. The form of "romantic" at play is clearly the sort found in married and engaged couples. It's no coincidence that so many same-sex couples believe themselves to be married or engaged. Thus I said:
So let me go out of my way to be very clear why your argument here does not succeed:
Your reasoning here is non-teleological, which is a problem for a Catholic. The relation of romance and sexual activity to the definition of a couple is not a matter of modal logic; it is a teleological notion. The epitome of a couple is a married couple, and marriage is the uniquely appropriate setting for sexual activity and procreation. A man and a woman who are dating or engaged are called a 'couple' because they partake, teleologically, in a possible future marriage. As their relationship matures it will accrue many of the trappings of a marriage, yet without becoming fully a marriage until they are wed. So romantic and sexual activity does not determine what makes two people a couple in the
modal sense, but rather in the
teleological sense. If two people are in no way ordered towards this epitome of marriage, then we do not call them a couple (and neither would we say that they are dating).
Of course the whole crux is that most secular people in our culture now believe that same-sex couples are truly ordered towards the epitome of marriage, and therefore Catholics will put scare quotes around the words that seculars take to be accurate. Catholics will speak of same-sex "marriage" or same-sex "unions," whereas seculars will speak of same-sex marriage and same-sex unions. Still, everyone knows what a "couple" is, and that it is teleologically related to romance and sex. Merriam-Webster's accurately captures usage, as dictionaries are supposed to do. And if you go ahead and look at what Merriam-Webster means by "marriage" and "engagement," you will find that, according to Merriam-Webster, a same-sex couple is a couple in the full sense, capable of so-called "marriage."
So your own definition from Merriam-Webster clearly falsifies your claim that sexual activity is unrelated to the definition of a "couple," for the definition, "Married, engaged, or otherwise romantically paired," is surely related to sexual activity.
Edit: I see you added a video from Fr. Mark Goring. He gives three examples. First, "a couple tomatoes." This is the adjective form I spoke of earlier, which is distinct from the noun form. Second, "There's a table for two here, is there a couple waiting? Yeah, my friend is here with her grandmother." This is confusing and equivocal, for the first sentence refers to a proper couple and the second sentence equivocates. We do not refer to grandmother and grandson as a couple, and this usage does not fit Merriam-Webster's definition (I gave a similar example earlier with mother & son). A seasoned restaurant employee would not have uttered the first sentence, and a seasoned speaker of English would not have responded "Yeah" to that question. Third, he gives the example of couples dancing, which fits the standard definition and does not help him to prove his point (dancers often
act as couples without
being couples). Goring effectively tries to disprove Merriam-Webster's definition, but he doesn't do a very good job.
Goring goes on to admit that it is a poor word choice for the document, and obviously he is right. Still, he needs to go a step further and answer the question that you failed to answer, "Okay, but
why?! If there is nothing incongruous about the language, or problematic about the logic, then why in the world would you not recommend or permit such a thing on your own authority?" (
link) It makes no sense to say that there is nothing wrong with the word and also say that it is a poor choice. If it is a poor choice then there is something wrong with it, and intellectually honest Catholics need to put these two puzzle pieces together.