c. 1400, neophite, "new convert" (modern spelling from 16c.), from Church Latin neophytus, from Greek neophytos "a new convert; one newly initiated," noun use of adjective meaning "newly initiated, newly converted," literally "newly planted," from neos "new" (see new) + phytos "grown; planted," verbal adjective of phyein "to bring forth, make grow," from PIE root *bheue- "to be, exist, grow."
Church sense is from I Timothy iii.6. Rare before 19c. General sense of "one who is new to any subject" is recorded from 1590s. As an adjective, "newly entered into some state," c. 1600.