1590s, "immortal, divine, of the quality of ambrosia;" see ambrosia + -al. The sense of "fragrant, delicious" is from 1660s. Other adjectives were ambrosiac (c. 1600); ambrosian (1630s).
Entries linking to ambrosial
ambrosia n.
1560s, "favored food or drink of the gods," from Latin ambrosia, from Greek ambrosia "food of the gods," noun use of fem. of ambrosios "divine," probably literally "of the immortals," from ambrotos "immortal, imperishable," from a- "not" (see a- (3)) + mbrotos, related to mortos "mortal," from PIE root *mer- "to rub away, harm" (also "to die" and forming words referring to death and to beings subject to death).
The name was applied to certain herbs by Pliny and Dioscorides; it has been used of various foods for mortals since 1680s (originally of fruit drinks); and was used figuratively for "anything delightful" by 1731.
-al 1
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).