From Dictionary dot com
Martial
adjective
1.
inclined or disposed to war; warlike:
The ancient Romans were a martial people.
2.
of, suitable for, or associated with war or the armed forces:
martial music.
3.
characteristic of or befitting a warrior:
Art
noun
1.
the quality, production, expression, or realm, according to aesthetic principles, of what is beautiful, appealing, or of more than ordinary significance.
(cut some off the second list because the last sentence seemed most appropriate)
By these two definitions, I'd have say - War tactics done at a level beyond the capability of the average person. "Characteristics" is a broad term that could include things like Honor and Ethics (just sayin)
When I (re)met my current instructor, he asked what I was trying to accomplish. I said that my employer expects me to be able to physically control people with as little damage as possible, and that is important, but my personal goal was to learn the most efficient and effective methods of breaking the human body (obviously under justified conditions and for the prevention of criminal violence). To me, that is what the PHYSICAL side of MA is.
I put forth a different definition for "art", this one supplied by Google:
"
A skill at doing a specified thing, typically one acquired through practice."
Examples give are "the art of conversation" and "the art of writing"
Synonyms given are: skill, craft, technique, knack, facility, ability, know-how.
I believe this is the appropriate definition when speaking of martial arts. Interestingly, this is a close parallel with the Chinese term "Kung-fu" which does not refer to fighting methods, but rather refers to skill (in any topic) acquired through hard work.
When speaking of martial arts, we are talking about methods and systems and techniques of combat. We are not speaking of an artistic endeavor in the sense of dance or painting. It has nothing to do with beauty or being asthetically pleasing. Any part of it that happens to strike your fancy as beautiful is a coincidence, or else is a deliberate detour from the original intentions of the martial art, to turn it into performance art.
In these discussions, people often get confused about that one term, art. They often translate that into a creative art or a performance art, and kata is often the first casualty of such a misunderstanding.
Martial arts are not about being asthetically pleasing while practicing combat-ish movements. Martial arts are any method or system or technique or body of techniques that, through diligent practice and hard work, develop a skill in some form of combat. That can be empty-hand or with weapons, both modern or ancient.