/ˌnēōˈnātl/
Adjective
1. Of or pertaining to the period of time immediately following birth, or to the newborn. (wiktionary.org)
2. of, relating to, or affecting the newborn and especially the human infant during the first month after birth. (merriam-webster.com)
3. (Pediatrics) Pertaining to the first four weeks after birth. (biology-online.org)
Word origin: From Greek neo-, comb. form of neos “new, young, youthful; fresh, strange; lately, just now,” + from Latin natalis “pertaining to birth or origin,” from natus, past participle of nasci “to be born.”