They are synonyms; either one can work. It is my feeling that inside the LDS Church culture, proselyte is more common. However, that’s definitely not the case in general. I used Mark Davies’s Corpus of Contemporary American English (COCA) and found that it includes 403 instances of some form of the word proselytize used as a verb, but only 1 instance of some form of proselyte used as a verb. (The search was proselyt.[v] for anyone who’s interested.)
Using Mark Davies’s corpus of LDS General Conference talks seems to confirm my hunch: I found 3 instances of some form of proselytize, while there were 158 instances of a verb form of proselyte. (Note that the raw numbers can’t be compared across corpora, but the ratios within each corpus are very telling.)
”Laser Jock, in response to my question about proselytize vs. proselyte.
So, I stand somewhat corrected. However, even though “proselyte” is a real word, it can still be added to the list of uncommon words/phrases that for some reason are quite common amongst Mormons.
