Dave of Balashon – Hebrew Language Detective (which I welcomed here and have since linked to less often than I should), has done a post—the last in a series on the five grains of the Land of Israel—on the Hebrew word כוסמת kusemet, which now means ‘buckwheat’ but once meant… well, that’s not clear, but I urge you to read his thoughts on the subject. And his final paragraph describes an interesting morphological/semantic split:
As we mentioned, Ben Yehuda made no reference to this usage. And in halachic literature, kusemet continued to refer to spelt. But even heavyweights such as these didn’t have control over the living language of Modern Hebrew. And the language seemed to come up with a solution of its own, and a strange on at that. Kusemet continued to be used for buckwheat, but the plural, kusmin כוסמין, was reserved for spelt – and you can actually find the two next to each other in the supermarket, even produced by the same company.
(In the course of his discussion, he links to this old LH post about emmer, spelt, and Italian farro; as usual, the thread wandered into a discussion of hats, snake goddesses, and what have you.)