There is a way to define things as what they are in themselves, or what they are in relation to other things as they are in themselves, and lastly, and likely the easiest, is what they are in relation to the concepts that lead to its definition.
For example, the word thought is defined as that which the mind thinks. Neither mind, nor thinking is defined in this definition of a thought, but rather thought is given a definition based on a system or series of concepts.
Another example, the word rock is defined as being stony, not only an object that may be of the earth. The former definition gives the quality of defining what a rock is in its relation to other things, such as a stone - though a kind of rock in itself, and the latter definition offers a formulation based on a system of concepts that lead to its definition. Of course, the rock is an object that may be of the earth, as in something that once was part of it and may now be dislocated from it. This is a weak definition, since there may be other objects that are of the earth but are not considered rocks, such as trees or flowers etc.
Finally, the defining of a thing as it is in itself is a deeply philosophical and at times existential act and exercise. It involves plunging into the depths of primary substances, concepts, to the point where the object is not defined by its relation to other tertiary substances or definitions but based on the most basic primal concepts, material, and formulations. What is a tree? Saying that a tree is a biological entity is simply placing it in a category and relating it to a system of concepts within groupings of science. But, what is a tree? Tell me, without relation to other things, tell me what it is in itself. Can you? Look at it.
What is a tree? This brings us to Aristotelian philosophy, where definitions are based on the assumption that things have a substance in and of themselves and not only in relation to other things - that they have a nature that is common. What is that nature? A tree by nature is something that grows, gives life, and provides shade, fruit, sustenance, and also material for possible use. That is a tree, for it has a purpose and a nature. Without the Aristotelian philosophical perspective, definitions simply turn on the mind’s assumption and knowledge of the unspoken nature of other things, when it is never directly addressed in any definition. It becomes a game of relationally to other things which are related to other things, until the dictionary relies on the mind of the reader to recall and inquire and remember, “Yes, there is a nature to things, that is in fact discoverable, a purpose to every thing created.”
What is a tree, however, in relation to God?
This is not Aristotelian, but a Christian method of defining, which has been explored to some extent on various topics, but never deliberately for all things. It brings us into the contemplation of the mind of God in creating all things and purposing creation.
What is a tree in relation to God?
This brings us into the contemplation, not only of the purpose of a tree in its relation to the created world in its entirety, but the purpose for which God created it.
Can you discover it?
In doing so, not only for a tree, but for all things, your mind will penetrate into mind of God in holy contemplation, lifted and caught up in the heavens in the genius and vastness of his mind.
What is a tree?
It is for Adam to have shade, for mankind to take fruit, and to rest.
Do not ask, what aspect of the nature of God it reflects, for it is a tree, and by happenstance may reflect his beauty and nature, but not by its nature, making these aspects insufficient or inconsequential to its definition, which demands its essence. For there is only one being that is made in the image of God, in his likeness and in his nature, that one can say reflects by its very being the nature of God.
It is mankind, both male and female.
What is man?
What are you?