"Recommend" is not a noun; it's a verb. Calling a recommendation a "recommend" has always grated on my nerves. It's like calling an invitation an invite. Invite is the verb. Invitation is the noun.
My professional analysis (and yes, I am an editor) is that most people are too stupid to distinguish between nouns (person, place, or thing) and verbs (action words). Return missionary is a complete misunderstanding of tense. The tense of "return" is called simple present. If one has completed a mission and has returned from that mission, one would use the simple past tense form, "returned."
My other theory is this is all part of cult-speak. Hassan talks about cults co-opting language and giving terms different meanings from what is customarily understood. Temple recommend is one of my favorite examples of this. In any other situation or conversation with any speaker of English, using "temple recommend" or "return missionary" would be corrected, or at least noted as poor grammar. However, that's the standard in mormonism and everyone understand what those terms mean. So the language is co-opted and means something different to mormons than it does to everyone else. This contributes to elitism and that warm, fuzzy feeling of being special.
I noticed that when I toured BYU many years ago -- religion classes especially aimed at "Return Missionaries." It bothered me then and it still doesn't sound right.
It evolves just like anything else. Today's rules of grammar will be seen as archaic in just a few decades.
What facinates me is how the Mormon Culture is forging a different and unique path. Imagine what Utah hicks would sound like if they had truly remained isolated in the mountain west.
It's hard to sandwich that hard "d" sound between two consonants. Leave it off verbally for enough generations and it begins to lose its place in written language as well.
I see this kind of thing all the time--unaccented -ed endings left off written words. People are just transcribing the way they speak: like "box set" instead of "boxed set.". I also see people dropping the -s from the ends of third person singular words, too, as in "She sit in the front row" or "The customer call me at noon.". Drives me bats, especially when the culprits claim to have been honors English students.
Cause (English speaking) TBMs don't care about grammar and don't bother to question things like this? If your native language is English (or if you are a fluent English speaker) yet you have never wondered about these types of simple things, (somebody who has returned from their mission called a 'return' missionary, or a temple recommendation called a temple 'recommend') you would never wonder or question anything else in the church.
Grammar problems? Please. Only people who need a reason to look down on others would ever worry about whether their grammar is correct.
Questioning someone's grammar neither makes you clever, nor more intelligent than the person you are questioning. Bad grammar doesn't make someone stick around in the church for longer, as one poster attempted to argue.
In this case, it is just a syllable that is dropped off the end of the word in the Utah accent. It isn't gone from the language, it is just mushed in the middle of all of the other syllables. Many dialects from all different types of languages do this.
Temple "recommend" is another good one. These sound strange to anyone "out in the world," but make insiders feel connected and accepted in their cultural group.
So, there I was, still finishing my undergrad and getting ready to apply for some stuff beyond college. I had left Mormonism about maybe 6 months prior to this. I went in to talk to my badass, exmo, linguist professor who was going to write me a letter of recommendation.
I sat down and said "Hey, thanks for writing me this letter of recommend."
Ugh...
I winced, he laughed, and then lectured me a bit on how people outside of Mormonism would not understand why I made that particular grammar error.