"One"

ichi | itsu | hito- | hito(tsu) | kazu [hi, hajime, osamu, makoto, and kazu] Original meaning: one, unity, first; to make one, to unify, to become one.

Other Japanese Terms for One:

Ittai: one body; a style or a form.
Isshun: instant, moment.
Isshokenmei ni: for life, with all one's might [Note: To practice wholeheartedly].
Toitsu suru: unity, coordinate, standardize.
Ichiritsu: uniformity, equality.
Kin'itsu: uniformity, equality, evenness.
Ichido: all (of us), all persons concerned.
Itten: the whole sky.
Hitotsu: one; the same.

Bibliography:
Halpern, Jack & Mizutani, Osamu. "The Kodansha: Kanji Learner's Dictionary". Kodansha International, New York 2002. ISBN: 4770028555

Disclaimer: The following interpretations, idea's, etc. are mine and mine alone. This is not any type of official view as to the meanings I give in the following paragraphs. Any omissions and errors are mine and I would enjoy feedback as to others opinions, feelings, and interpretations for this is a teaching/learning forum.

Ittai: one body; a style or a form.
Ittai or "one body" is the culmination of training and practice in a singular form such as the fighting art of "Ti" where training the mind-body-spirit to achieve "one" with the Way is the path we chose to follow in becoming enlightened. In this particular case, i.e. the practice of "Ti", we use a specific and unique form or style of practice to gain experience and knowledge.

Isshun: instant, moment.
To achieve the ability to remain in the present moment, the instant of life we experience in real time. This is not dwelling on the past or contemplating the future but to live in this instant as each present moment comes to life and immediately exits to the past. This instant, this present time, and this one moment is the only moment as all others are mists in the wind.

Isshokenmei ni: for life, with all one's might [Note: To practice wholeheartedly].
In the practice of ti-jutsu one must consider that in a moment a life can be affected by the circumstances we encounter in our day-to-day lives. It is that "one" moment where we will act and that action will change the course or path we travel irrevocably. This is all the more reason to practice and train with all one's might or with intent to be consistent and diligent; to practice wholeheartedly.

Toitsu suru: unity, coordinate, standardize.
When I think of "standardize" or to standardize something it brings to mind the system of Ti. In other words the kihon, kata, and kumite of the Okinawan Fighting Arts, i.e. Ti. History has shown that the most effective means of combative training with out actually being in combat is to drill. The standards set by our forefathers through out various cultures over a long and illustrious history indicate that to use standardized methods is best in reaching "one" with all the aspects of training and practice required to achieve victory in combat as well as life.

Ichiritsu: uniformity, equality.
Equality is understanding others so we can come to realize that we are all the same and that understanding provides for unity which can result in a peaceful coexistence in the Universe. This is very important as the gokui and means of training intended by Tatsuo Sensei.

Through the uniformity of mutual understanding we achieve enlightenment where the need to resolve anything with conflict is no longer necessary.

Kin'itsu: uniformity, equality, evenness.
Equality of mankind or humanity does not mean we lose site of our uniqueness. It simply means we understand our uniqueness and through understanding we come to understand what it takes for us as individual to co-inhabit the Earth with out conflict. If I understand another's way of life then I can adjust myself accordingly when my aura comes in contact with another's.

Evenness is the balance we attain through our understanding of humanity so we are more connected with the threads of the Universe or the Tao which connects us to the one or the "void" that is the Tao. No resistance so the energies flow with one another equally and in balance.

Ichido: all (of us), all persons concerned.
The Kenpo Gokui as meant to be understand from Tatsuo Sensei means that to understand all others to unify humanity in the Tao means to be concerned for all persons in humanity. I would venture to go a bit further to say we must understand all entities concerned be it a tree, a rock, animals, or mankind/humanity.

Itten: the whole sky.
I believe this is representative to being one with the Universe. As the gokui says to have heart as heaven and earth with ki flowing as does the flow of the moon and sun while achieving balance in all things and with all of life under the heavens. The whole of the void, the Tao, the Way, as in life.

Hitotsu: one; the same.
To be "one"; to be the same in all things; to achieve serenity and enlightenment; to be "one" with the Tao; to be "one" with the universe; to be "one" with all life forces; to be "one" with mind-spirit-body; to achieve "one" with the rhythm of the Universe. What a wonderful achievement in our lifetime regardless of which one we are in at this "present moment!"

To be unique yet the same.

What I have posted here is just the tip of the iceberg. I only hope that this tickles you desire to go further and find your own answers to all the questions life brings. I can only say that I am hopeful that the answers I have discovered to date resolve the "One question of what it is all about."