A proportion of the names in the Book of Mormon end in “-iah” or “-ihah”. Hugh Nibley notes how these compound names were peculiar to Palestinian names of Lehi’s time but not so prevalent other times.
“The strong tendency to end in -iah is very striking, since the vast majority of Hebrew names found at Lachish [i.e., from records contemporary with Lehi] end the same way, indicating that -iah names were very fashionable in Lehi’s time.” Since that was written our view has been confirmed by a study made by D. W. Thomas, who noted that a “striking” peculiarity of Hebrew names in the age of Jeremiah is “the many personal names which end in -iahu.” Thus Reifenberg lists from the ancient Hebrew seals of the time such names as Jekamjahu (Jekamiah), Shepatjahu son of Asjahu, Jaazanjahu, Gadjahu (cf. Book of Mormon Gadiandi, Giddianhi), Hilkjahu, Gealjahu, Alijahu, etc. This -iahu ending (German -jahu) is our biblical -iah, -ijah, and by a common metathesis also becomes the extremely common Book of Mormon name ending -ihah.– Hugh Nibley – An Approach to the Book of Mormon
How would Joseph Smith know about compound names and specifically those prevalent in Lehi’s time?