There are some other things that help define a character. Names are one thing. Choosing how to name your characters can be sometimes harder than writing the synopsis. Well, maybe not. I spend a lot of time naming characters and looking through books of names including those like New Age Books. Once I had a computer program to help with this but that was many computers ago and the program came on one of those large floppy discs. Sometimes the name comes easy. When I was writing The Warrior of Bast, I needed names that sounded like they could be coming from Egypt and so I sat with books on Egypt and looked at the names of the pharaohs and queens and then did variations. The characters in The Henge Betrayed series are plays on my grandchildren's names. mostly with new endings added to their names, thus Brandon became Brandien, Kyla became Kylandra and so forth. Sometimes when I'm reading books particularly those set in historical periods one sees names that don't fit what we think of as being pleasant names today but in the time period of the historical the names are perfectly fine. Or names that once were men's names are now used for women. So one has to decide to be true to the period or true to today.
Another way of defining a character is posture -- How does a person stand. Do they slouch or stand like there's a rod in their spine. Are their shoulders hunched or straightened. I once read a description that was sort of like this. He walked as though he had no bones. Does that mean graceful or did he ooze across the stage. Posture can also show a person's mood. Ways of moving also do this. Does your heroine always strice or does she mince. Does he walk with a heavy tread? A lot about a person's nature can be shown by the way they walk or stand.
What about expressions. What does this statement make you think. He wore his perpetual sneer. Doesn't make me what to like this person. She was never without a smile. Eyes danced with laughter. Just seeing how another person views the expressions a character wears can give a picture in an instant.
There are more ways that I'll get to another time. Just remember when you're showing your characters try to show more than a static description. If possible avoid having them look into a mirror.