Why does the Book of Mormon seem to understand the word “Rameumptom” has Hebrew roots meaning a high/holy stand?

In several places in the Book of Mormon a word or name is followed by its interpretation. One example is that of Rameumptom.

Alma 31:13 reads:

For they had a place built up in the center of their synagogue, a place for standing, which was high above the head; and the top thereof would only admit one person.

Later in the chapter the name and interpretation are given:

Now the place was called by them Rameumptom, which, being interpreted, is the holy stand.

This would be a bold move by Joseph Smith if he had written the Book of Mormon himself because the interpretation could be proved wrong. However the Book of Mormon Onomasticon explains how it is spot on:

The first element of the name is most likely related to HEBREW rām, “to be high, to be exalted,” and rāmâ, “eminence, high place,” the same root that appears in the biblical geographic name RAMAH, “hill” (cf. Book of Mormon RAMAH). RAMEUMPTOM could be a noun chain with râme as a masculine construct plural, meaning “the elevations of.” The -umptom would then be a nomen rectum, possibly from HEBREW ʿōmed , “place, position, location,” with either a pronominal suffix, analogous to the 3rd person plural possessive pronoun -ām, or with the nominalizing ending –ōm. The latter ending is probably to be preferred because of the analog form in Arabic, ʿumdān “standing.” Given these two HEBREW lexemes, rām and ʿōmed, the meaning of RAMEUMPTOM would then be “the heights/ elevations of (their) stand” (RFS), a definition that accords well with the interpretation that the Book of Mormon writers provided.
– Book of Mormon Onomasticon – Rameumptom

Why would Joseph Smith intentionally include the definition of the word Rameumptom? Wouldn’t this leave him open to being exposed? How did he manage to create a word with the correct Hebrew meaning?

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