The Ankh, also known as key of life, the key of the Nile or crux ansata (Latin meaning "cross with a handle"), was the ancient Egyptian hieroglyphic character that read "life", a triliteral sign for the consonants ꜥ-n-ḫ. It represents the concept of eternal life, which is the general meaning of the symbol. The Egyptian gods are often portrayed carrying it by its loop, or bearing one in each hand, arms crossed over their chest.
The origin of ankh is highly debated and it is represented by an oval or point-down teardrop set atop a T shape. Wikipedia, Ankh
Athanasii Kircheri
Concerning the Hermetic Cross, which we commonly call the Ankh in this Work, and its secret meaning in the Hermetic work.
Hermes Trismegistus, as the first inventor or restorer of letters, so also the establisher of Hieroglyphic characters, so that he might express by a wonderfully devised symbol what lies most hidden in the World, expressed everything by a single character, which they also call the Hermetic Cross (we call it Isiac, or Ankh, because it is almost always seen carried in the hand in Egyptian sacred rites). This character they held in such great veneration that they thought nothing could be rightly accomplished without it; and it was a most powerful amulet, and a character fabricated according to the example of nature with a wonderful subtlety of genius, the sole guide and light for showing the way to happiness; whose virtue Marsilio Ficino describes especially in his book on propagating life from heaven in these words.
The more ancient Egyptians, as we read in a certain Arab Collection, placed the figure of the Cross before all things; through which bodies act by Virtue upon the already diffused surface, but the first surface is described by the Cross, for it first of all has length and breadth, and this is the first figure, and of all straight lines the most straight, it contains four right angles; but the effects of the celestial bodies result especially through the straightness of the rays and angles, for then the stars are especially powerful, when they hold the four angles of Heaven, indeed the cardinal points, namely of the East and West, and of the middle of Heaven on both sides; thus truly disposed, they cast their rays into each other, so that they form a Cross from them. Therefore, the Ancients said the Cross to be a figure made both of the strength of the stars, and the receptacle of their strength, and they signified all the secrets of the World by it.
But since we have most fully demonstrated everything about the Ankh in the "Pamphilian Obelisk" 1. 2., I have thought it superfluous to repeat these things in this place; therefore I refer the Reader to it; it is our task to explain here what secret mysteries of the great art the said Cross signifies, which will then be done opportunely, when we shall first have shown the structure of the whole Hermetic or Mercurial character.
Thus, it should be known that Hermes, while noting the greatest connection of the celestial bodies, and therefore that all things in all things are in some way hidden, established two Astronomies, celestial and elementary. In the celestial he considered the order, connection, properties, and influences; in the Elementary he considered all the same things, but in his own way; and thus there is nothing in the lower world of elementary mixture that could not be found in the celestial, by a certain analogical comparison. These are in the upper world; the same are in the lower world, as has been abundantly demonstrated in various places of this Work. Therefore, when he had considered these things, he devised a hieroglyphic character, which he called Hermetic, Tautic, or Mercurial, in which he comprehended the secrets of both Astrologies, by a certain mystical reasoning and wonderful artifice. And although in hieroglyphics this character is exhibited with a somewhat rougher execution, it nevertheless has its hidden proportions, by which the innermost actions of the Mundane spirit might be expressed. But I will show the structure.
Diagram Explanation
Let a straight line AB be drawn on some plane, which you will divide into nine equal parts, almost in the same way that the Egyptians divided the expanse of the Sidereal World. This being done, count three parts out of 9, from A upwards to point E, through which point you will draw line DC, intersecting line AB at right angles; which line indeed occupies two parts on each side out of 9, such are lines ED, and EC. Again, from point E upwards you will count three parts out of 9, up to point I; at which you will place the compass, and with an interval of two parts, such as the whole line AB has 9, let circle PMN be described. This also being done, let the compass be placed again at the extreme point, and with an interval of two parts, such as line AB contains nine, let semicircle XYZ be described: the semicircle having been described, let a line RG be drawn from A, the other extreme, four parts out of nine long, so that two parts exist on each side; and G having placed the compass at points S, and T, with interval TA, and SA, let semicircles RVA, and AHG be described on each side; and you will have the Hermetic character described according to its due proportion, and in every way agreeing with the symmetry of the mundane body. Moreover, nothing remains, unless we now explain its mysteries step by step, which indeed we will perform part by part."
"The affinity, properties, and nature of the remaining metals to gold and silver, what should be added to or taken away from each, so that they may not degenerate from the Sun or Moon, the Hermetic character beautifully denotes, depicted by a certain secret similitude of the celestial economy, as regards its situation, location, and nature, from the knowledge of which one is led into the right path that individual metals can be exalted in the Sun and Moon." [Partial translation about the hieroglyphic monad from "Athanasii Kircheri Soc. Iesu Oedipi Aegyptici. Tomi Secundi."]
See Also
Breath of Life
Celestial Outreach
Latent Element
Life
Life Force