Maia was the oldest and most beautiful of Atlas and Pleione's seven daughters. Timid, she lived alone in an Arcadian cave until Zeus met and fell in love with her, beginning an affair in secret from Hera, his wife. Of their affair came a son, Hermes, who robbed Apollo of some cattle as an infant. Maia also later took in Arcas, a son from another of Zeus' affairs, and raised him as her own after Hera had punished Arcas' mother, Callisto, with death.
Magaera was the grudging sister of the three Furies, whose breath burned, whose blood poisoned, whose heads were crowned with serpent wreaths. Products of the blood shed during Uranus' castration by his son to avenge the death of his sibling, the Furies' existences were consumed by the shared mission of wreaking vengeance for crimes pertaining to murder, injustice, perjury, ingratitude or disrespect that somehow slipped by society's provisions for justice. They punished offenders mercilessly until they displayed remorse -- even if they had to continue punishing offenders in death.
Metis, daughter of Oceanus and Tethys, was another of Zeus' many lovers as well as an adviser to him during the Titan War. Her cunning and wisdom assisted him through many important feats such as tricking Kronos into regurgitating the children he had swallowed. When Metis became pregnant with Athena, Zeus feared prophecies that the child she bore would be more powerful than Zeus -- so he swallowed her whole before the child could be born. Nevertheless, the child, Athena, emerged from his head fully formed and fully armored, and Metis continued to provide Zeus with good counsel from inside his head.
Led by Zeus, the Goddesses of Fate, the Moirae -- whose collective name means "Allotted Portions" -- were a group of goddesses who designated every man's inevitable fate. When each person was born, they would allot a designated amount of thread to his life, follow every step he took and bring about appropriate consequences for his choices and actions.
Inventor of words, Mnemosyne was responsible for ensuring that the humans memorized and recalled the myths of the gods in the time when writing did not yet exist. Nine months after Zeus had slept with her for nine consecutive nights, she gave birth to nine daughters who came to be known as the Muses. The daughters played, danced, sang and provided entertainment for gods and goddesses, serving as sources of creative and artistic inspiration.
Meiboia (the Bee Goddess); Meilichia and Melinoe (both Goddesses of the Underworld); Molpadia (Goddess of Childbirth); Mystis (Goddess of Teaching); Methe (Goddess of Drunkeness); and Makaria (Goddess of Blessed Death) are more Greek goddesses whose names begin with the letter "M."