Your deer question is simply answered by the fact that yes, the word 'deer' may broaden to include moose, caribou, etcetera but the word 'deer' doesn't exist on its own.
Just to be clear -- my understanding is that
deer used to be more inclusive before it came to be used for the animals we know today as deer. Provided we have names for the other animals that used to be
deer, we can have a gain in meaning.
A personal anecdote might help. When I moved to North Dakota I knew the Big Dipper and that was about it. But the sky was darker here and I began to learn constellations. (To give you an idea of how impoverished my recognition of constellations had been, I cane date the first time I
identified so basic a constellation as Orion. This was in late October 1990.) Now here's the thing: once I learned some constellations and stars, I not only noticed the patterns more but also the colors of individual stars. I could
see the redness of Betelgeuse and Antares. Formerly I think I thought of stars as basically just points of white light.
So the point is that when I had
names for these individual patterns or specific stars, my perception changed. When I had words for these things (patterns, points) I saw them, in a way for the first time. This impressed on me something of the value of protecting words with particular meanings. If I grasp the traditional meaning (seen in innumerable poems) of
gay, I may have an enhanced awareness of a particular state of bright, carefree wellbeing. If I feel that exact emotional state, I can
put a word to it and thereby understand my own feelings better. But, conversely, if that particular meaning is eclipsed in usage, I may lose the capacity to perceive something about my own feelings.
Look, here's another example. Some of you are old enough to remember when a German word began to appear in English writing:
schadenfreude. Some of us first then realized that we indulged this rather ignoble emotion, and, so, learned something about ourselves. If this word disappeared from our vocabulary, what word would we have to express just that emotion that we may have felt but not
recognized?
Or the Japanese
mono no aware has made an entrance into usage by English speakers who do not know Japanese. It captures something we may have inchoately felt but not really recognized, a sort of sweet yet sad pathos as we consider the transience of things such as tree blossoms. My experience of life is enhanced. I don't know of any English word or expression that would serve as a succinct substitute. So now if people start using the Japanese expression to mean just "sadness," people would stand to lose some of the potential meaning that, I would say, is
there, not "projected onto" nature but belonging to it. The Greek myth of Persephone, by the way, means more to me now that I "get"
mono no aware. The myth is not just an expression of seasonal changes, but a story (I would suggest) about something for which the Greeks didn't have a word or phrase (so far as I know) -- but the Japanese did.
Good poetry protects, preserves, transmits to readers who receive it, a pure or purified language. To be sure a poet may invent words or see the potential of existing words for conveying inner states that he or she has had and that now maybe can be shared with others. I might not be able to be a poet but perhaps I can have something of a proper reverence (not idolatry) for language.
Owen Barfield's
Poetic Diction has lit up things like these for quite a few readers.