Following the Greek Septuagint or Latin Vulgate or both, the earlier pre-1611 English Bibles (Wycliffe's, Tyndale's, Coverdale's, Matthew's, Great, Taverner's, Geneva, and Bishops') all had unicorn [singular] at Deuteronomy 33:17. At this verse, Lancelot Brenton’s 1851 English translation of the Septuagint has “unicorn” [singular]. The 1569 Spanish Bible and 1602 Spanish Valera has unicornio [singular] at this verse. The 1611 KJV changed this noun that was singular in number in the Hebrew Masoretic text and in all the earlier English Bibles to a plural. Either the 1762 Cambridge standard KJV edition or the 1769 Oxford standard KJV edition added the following marginal note for the word unicorns: “Hebrew an unicorn.” Other KJV editions that had marginal notes such as the 1810, 1821, 1835, 1857, 1865, and 1885 Oxford editions, the 1853 American Bible Society standard edition, the 1769, 1844, 1872, 1887, and the 2005 Cambridge editions, and the 2002 Zondervan KJV Study Bible have this same marginal note at this verse. This marginal note in standard editions of the KJV affirms with the earlier pre-1611 English Bibles, the 1602 Spanish Valera, and the 1657 English translation of the Dutch that the Hebrew word was singular in number. There is a plural form for this Hebrew word, which was not used at this verse (Deut. 33:17). The number of the Hebrew word at this verse is the same as its number at Numbers 23:22 [singular]. In his 1828 Dictionary, Noah Webster defined an as “one; noting an individual, either definitely known, certain, specified, or understood; or indefinitely, not certain, known, or specified.” Webster noted that “an, a and one, are the same word, and always have the same sense.” Webster’s New Twentieth-Century Dictionary noted that a is “an abbreviation of Anglo-Saxon an or ane” with the meaning “one.” Therefore, “an” unicorn has the same meaning or sense as “one” unicorn, affirming that the Hebrew word is singular in number. Thus, the Bible in the original language referred to the strength of one reem (Num. 23:22) and to the horns of one reem (Deut. 33:17). Rosh Hashanah [the Babylonian Talmud] as translated into English by Maurice Simon also indicated that the Hebrew word is singular in number: “the horns of a reem” (p. 116). There is also a reference to Deuteronomy 33:17 in the comments on Psalm 22:21 in the Longer Commentary of Rabbi David Kimchi on the First Book of Psalms as translated into English by R. G. Finch that affirms that the Hebrew word is singular in number [“the wild ox will gore with his horns, as it says (Deut. 33:17)” (p. 104). Another reference to this verse is also found in David Kimchi’s Commentary upon the Prophecies of Zechariah as translated into English by Alexander M’Caul in 1837, and it also indicates that the Hebrew word is singular in number (p. 28).
The context of the verse in Deuteronomy also supports the view that this animal had more than one horn. In the context, the “them” of this verse refers back to “horns.“ William Houghton observed: "The two horns of the reem are 'the ten thousands of Ephraim and the thousands of Manasseh'--the two tribes which sprang from one, i.e. Joseph, as two horns from one head" (Hacket, Smith's Dictionary of the Bible, p. 3351). Likewise, H. B. Tristram commented: “For the two horns of the reem are the ten thousands of Ephraim, and the thousands of Manasseh, both growing out of one head, Joseph. This, then, entirely sets aside the fancy that the rhinoceros, which the Jews could scarcely have known, or any one-horned creature, is intended” (Natural History, p. 146). Wiley noted that "the emblem of Joseph was the re'em; and his two powerful sons, Ephraim and Manasseh, were typified by two horns" (Bible Animals, p. 429). John Gill noted that the horns “are figures of the power and strength of the tribes of Ephraim and Manesseh.“ T. E. Espin asserted that the “tribes of Ephraim and Manasseh are represented by the two mighty horns of the beast” (Cook, Bible Commentary, I, p. 743). Ellicott’s Commentary mentioned “the two-horned power of Joseph” (II, p. 94). The Companion Bible [KJV] suggested that the “horns” are “put by figure Metonymy” for Ephraim and Manasseh (p. 287). These observations concerning the context are also in agreement with another verse (Num. 14:4) which stated: “For the children of Joseph were two tribes, Manasseh and Ephraim“. In contrast, KJV-only authors seem to ignore this credible evidence from the context that indicates that this animal had two horns. Should the context be considered the decisive factor in deciding whether the animal had more than one horn or not?