type of peach with smooth skin and firmer pulp, 1660s, noun use of adjective meaning "of or like nectar" (1610s; see nectar + -ine (1)). Probably inspired by German nektarpfirsich "nectar-peach." Earlier in English as nectrine.
1550s, from Latin nectar, from Greek nektar, name of the drink of the gods, which is perhaps an ancient Indo-European poetic compound of nek- "death" (from PIE root *nek- (1) "death") + -tar "overcoming," from PIE root *tere- (2) "cross over, pass through, overcome." Sense of "any delicious drink" is from 1580s. Meaning "sweet liquid in flowers" first recorded c. 1600.
also -in, adjectival word-forming element, Middle English, from Old French -in/-ine, or directly from Latin suffix -inus/-ina/-inum "of, like," forming adjectives and derived nouns, as in divinus, feminus, caninus; from PIE adjectival suffix *-no- (see -en (2)).
The Latin suffix is cognate with Greek -inos/-ine/-inon, and in some modern scientific words the element is from Greek. Added to names, it meant "of or pertaining to, of the nature of" (Florentinus), and so it also was commonly used in forming Roman proper names, originally appellatives (Augustinus, Constantinus, Justinus, etc.) and its descendants in Romanic languages continued active in name-forming. The Latin fem. form, -ina, was used in forming abstracts (doctrina, medicina). Relics of the attempt to continue a distinction between Latin -ina and -inus account for the English hesitation in spelling between -in and -ine.