Ambrosia is sometimes depicted in ancient art as distributed by a nymph labeled with that name and a nurse of Dionysus. In the myth of Lycurgus, the king attacked Ambrosia and Dionysus' entourage, causing the god to drive Lycurgus insane.
Ambrosia is very closely related to the gods' other form of sustenance, nectar. The two terms may not have originally been distinguished; though in Homer's poems nectar is usually the drink and ambrosia the food of the gods; it was with ambrosia Hera "cleansed all defilement from her lovely flesh", and with ambrosia Athena prepared Penelope in her sleep, so that when she appeared for the final time before her suitors, the effects of years had been stripped away, and they were inflamed with passion at the sight of her. On the other hand, in Alcman, nectar is the food, and in Sappho and Anaxandrides, ambrosia is the drink. A character in Aristophanes' Knights says, "I dreamed the goddess poured ambrosia over your head—out of a ladle." Both descriptions could be correct, as ambrosia could be a liquid considered a food (such as honey).
The consumption of ambrosia was typically reserved for divine beings. Upon his assumption into immortality on Olympus, Heracles is given ambrosia by Athena, while the hero Tydeus is denied the same thing when the goddess discovers him eating human brains. In one version of the myth of Tantalus, part of Tantalus' crime is that after tasting ambrosia himself, he attempts to steal some away to give to other mortals. Those who consume ambrosia typically had not blood in their veins, but ichor, the blood of immortals.
Both nectar and ambrosia are fragrant, and may be used as perfume: in the Odyssey Menelaus and his men are disguised as seals in untanned seal skins, "...and the deadly smell of the seal skins vexed us sore; but the goddess saved us; she brought ambrosia and put it under our nostrils." Homer speaks of ambrosial raiment, ambrosial locks of hair, even the gods' ambrosial sandals.
Among later writers, ambrosia has been so often used with generic meanings of "delightful liquid" that such late writers as Athenaeus, Paulus and Dioscurides employ it as a technical terms in contexts of cookery, medicine, and botany.Pliny used the term in connection with different plants, as did early herbalists.
W. H. Roscher thinks that both nectar and ambrosia were kinds of honey, in which case their power of conferring immortality would be due to the supposed healing and cleansing powers of honey, which is in fact anti-septic, and because fermented honey (mead) preceded wine as an entheogen in the Aegean world; on some Minoan seals, goddesses were represented with bee faces (compare Merope and Melissa).
The concept of an immortality drink is attested in at least two Indo-European areas: Greek and Sanskrit. The Greek ἀμβροσία (ambrosia) is semantically linked to the Sanskrit अमृत (amṛta) as both words denote a drink or food that gods use to achieve immortality. The two words appear to be derived from the same Indo-European form *ṇ-mṛ-tós, "un-dying" (n-: negative prefix from which the prefix a- in both Greek and Sanskrit are derived; mṛ: zero grade of *mer-, "to die"; and -to-: adjectival suffix). A semantically similar etymology exists for nectar, the beverage of the gods (Greek: νέκταρ néktar) presumed to be a compound of the PIE roots *nek-, "death", and -*tar, "overcoming".
Other examples in mythology
Thetis anoints Achilles with ambrosia, by Johann Balthasar Probst (1673–1748)
In one version of the story of the birth of Achilles, Thetis anoints the infant with ambrosia and passes the child through the fire to make him immortal but Peleus, appalled, stops her, leaving only his heel unimmortalised (Argonautica 4.869–879).
In the Iliad xvi, Apollo washes the black blood from the corpse of Sarpedon and anoints it with ambrosia, readying it for its dreamlike return to Sarpedon's native Lycia. Similarly, Thetis anoints the corpse of Patroclus in order to preserve it. Ambrosia and nectar are depicted as unguents (xiv. 170; xix. 38).
In the Odyssey, Calypso is described as having "spread a table with ambrosia and set it by Hermes, and mixed the rosy-red nectar." It is ambiguous whether he means the ambrosia itself is rosy-red, or if he is describing a rosy-red nectar Hermes drinks along with the ambrosia. Later, Circe mentions to Odysseus that a flock of doves are the bringers of ambrosia to Olympus.
In the Odyssey (ix.345–359), Polyphemus likens the wine given to him by Odysseus to ambrosia and nectar.
In the story of Cupid and Psyche as told by Apuleius, Psyche is given ambrosia upon her completion of the quests set by Venus and her acceptance on Olympus. After she partakes, she and Cupid are wed as gods.
Some ancient Egyptian statues of Anubis read,"...I am death...I eat ambrosia and drink blood..." which hints that ambrosia is a food of some sort.
In the Aeneid, Aeneas encounters his mother in an alternate, or illusory form. When she became her godly form "Her hair's ambrosia breathed a holy fragrance." 
Lycurgus, king of Thrace, forbade the cult of Dionysus, whom he drove from Thrace, and attacked the gods' entourage when they celebrated the god. Among them was Ambrosia, who turned herself into a grapevine to hide from his wrath. Dionysus, enraged by the king's actions, drove him mad. In his fit of insanity he killed his son, whom he mistook for a stock of ivy, and then himself.
Amrita, of Hindu mythology, a drink which confers immortality on the gods, and a cognate of ambrosia
^Ruth E. Leader-Newby, Silver and Society in Late Antiquity: Functions and Meanings of Silver Plate in the Fourth to Seventh Centuries (Ashgate, 2004), p. 133; Christine Kondoleon, Domestic and Divine: Roman Mosaics in the House of Dionysos (Cornell University Press, 1995), p. 246; Katherine M. D. Dunbabin, Mosaics of the Greek and Roman World (Cambridge University Press, 1999), pp. 136, 142, 276–277.
^"Attempts to draw any significant distinctions between the functions of nectar and ambrosia have failed." Clay, p. 114.
^Carl A.P. Ruck and Danny Staples, The World of Classical Myth 1994:26.
^Mallory, J. P. (1997). "Sacred drink". In Mallory, J. P.; Adams, Douglas Q. (eds.). Encyclopedia of Indo-European Culture. Taylor & Francis. p. 538. Mallory also connects to this root an Avestan word, and notes that the root is "dialectally restricted to the IE southeast".
^Odyssey xii.62: "the trembling doves that carry ambrosia to Father Zeus."
^Harmer; Burder; Paxton & Roberts (1839). Illustrations of the Holy Scriptures, derived principally from the manners, customs, rites, traditions and works of art and literature, of the eastern nations. Brattleboro Typographic Company.
Clay, Jenny Strauss, "Immortal and ageless forever", The Classical Journal77.2 (December 1981:pp. 112–117).