In the translation of Mansi, Sacrorum Conciliorum Nova et Amplissima Collectio, xiii 277C-E (extracts from the Council of Hieria [754] that were read out during the Second Council of Nicea [787]), we have an instance of the plural of “cherub” being translated as cherubims, not cherubim:
[277C-E] How indeed do they dare depict through the gross art of the pagans
the all-praised Mother of God who was overshadowed by the plenitude of
divinity, through whom an unapproachable light did shine for us, who is higher
than the heavens and holier than the cherubims? Or [the
saints] who will reign with Christ, and side beside Him to judge the word, and
share in His glory (of whom Scripture says that the world was not worthy of
them)-are they not ashamed to depict them through pagan art? For it is not
lawful to Christians who believe in the resurrection to adopt the customs of
demon-worshipping gentiles, and to insult by means of inglorious and dead
matter the saints who will be adorned with so much glory. Indeed, we do not
accept from aliens the proof of our faith: yea, when the demons addressed Jesus
as God, he rebuked them, because He deemed it unworthy that demons should bear
testimony concerning him. (Leslie Brubaker and John Haldon, Byzantine and
the Iconoclast Era c. 680-850 [Cambridge: Cambridge University Press, 2011],
195, emphasis added)
Here is the scan of the section (click to enlarge):
This is significant as the earlier editions of the
Book of Mormon rendered the plural of “cherub” as “cherubims.” While
some have argued this was a KJV error that Joseph Smith carelessly carried over
into the Book of Mormon, using “-ims” to render a plural is an acceptable practice
in English translations of Hebrew words. For more, see:
Seraphim(s), Cherubim(s), and the Book of Mormon