By A.E. Waite (1911), tarot card illustrations by Pamela Colman Smith (1911)
Hidden enemies, danger, calumny, darkness, terror, deception, occult forces, error.
Divinatory Meanings – Reversed
Instability, inconstancy, silence, lesser degrees of deception and error.
The distinction between this card and some of the conventional types is that the moon is increasing on what is called the side of mercy, to the right of the observer. It has sixteen chief and sixteen secondary rays. The card represents life of the imagination apart from life of the spirit. The path between the towers is the issue into the unknown. The dog and wolf are the fears of the natural mind in the presence of that place of exit, when there is only reflected light to guide it.
The last reference is a key to another form of symbolism. The intellectual light is a reflection and beyond it is the unknown mystery which it cannot shew forth. It illuminates our animal nature, types of which are represented below–the dog, the wolf and that which comes up out of the deeps, the nameless and hideous tendency which is lower than the savage beast. It strives to attain manifestation, symbolized by crawling from the abyss of water to the land, but as a rule it sinks back whence it came. The face of the mind directs a calm gaze upon the unrest below; the dew of thought falls; the message is: Peace, be still; and it may be that there shall come a calm upon the animal nature, while the abyss beneath shall cease from giving up a form.
18. The Moon. Some eighteenth-century cards shew the luminary on its waning side; in the debased edition of Etteilla, it is the moon at night in her plenitude, set in a heaven of stars; of recent years the moon is shewn on the side of her increase. In nearly all presentations she is shining brightly and shedding the moisture of fertilizing dew in great drops. Beneath there are two towers, between which a path winds to the verge of the horizon. Two dogs, or alternatively a wolf and dog, are baying at the moon, and in the foreground there is water, through which a crayfish moves towards the land.
By S. L. MacGregor Mathers, c 1888
The Moon – Twilight, Deception, Error.
Divinatory Meanings – Reversed
Fluctuation, slight Deceptions, Trifling Mistakes.
Symbolism of the Keys
The Moon – The moon shining in the heavens, drops of dew falling, a wolf and a dog howling at the Moon, and halted at the foot of two towers, a path which loses itself in the horizon (and is sprinkled with drops of blood, a crayfish emblematic of the sign Cancer, ruled over by the Moon, crawls through water in the foreground towards the land). It symbolises Twilight, Deception, and Error.
General Book of the Tarot
By A. E. Thierens, 
Description and Meaning
Everything that has been said in astrology about the Moon might be repeated here, as there exists no controversy whatever on the point of identity. “The card represents life of the imagination apart from life of the spirit.” (Waite)
This card consequently means the life of the soul in particular, the feelings and sentiments, emotions (not only fear, etc.), changes wrought in existence by them, water and the female element in general. In the horoscopic figure it may be the mother or some other woman prominent in the life of the querent; it may signify women in general (and morally or psychically, while Saturn means physical woman). It is the sign of panta rei: everything passing, flowing or ebbing away in life, consequently uncertainty. It may relate to dreams, to exhibitions, popular plays, and games, theatres, and to the lower class of people. Physically it means the brain and the stomach.
The hieroglyphic value of the Hebrew letter Tzaddi, connected with this card, “is the same as that of Thet (ninth card) . . . which perhaps may account for the relationship of the Moon with that house, as pointed out by us before. It should mean a term, an aim, an end.” (Papus) But this does not make it much clearer.
Papus has only one good thing on it, and after all this is only on a particular and not very high level: “Servile spirits (the dog), savage souls (the wolf), and crawling creatures (the crayfish) are all present watching the fall of the soul, hoping to aid in its destruction.” That is true. And it may happen to us, that a lower current of the Moon brings our way people who have no higher aim than to ‘aid in our destruction’ even if we ourselves have no intention whatever of ‘falling’.
By Paul Foster Case (1933)
18, La Lune
Although this card is named “The Moon,” it is really related to the zodiacal sign Pisces, through the letter Qoph, which corresponds to that sign. Its meanings are, in divination, clearly traceable to the 12th house influence of the sign Pisces. This card is very sensitive to the influence of other cards around it in a layout.
Voluntary change, advance into a wider field of activity, but an advance made primarily because the Querant is unhappy in, or dissatisfied with his present position. There is always an element of uncertainty in matters represented by this card.
It stands for error, lying, deception; for limitations resulting from the Querant’s own lack of judgement or his want of self-control; for difficulties brought about by the machinations of hidden enemies.
More information on The Moon Tarot card.