Static characters end with the same inner traits and world view as they begin the story with. In other words, whatever they go through or experience, whatever tragedies or adventures they have, the end result is that they still feel about things, react to things and view things the same way as they did from the start. This is fine for specific kinds of fiction. Other kinds of fiction require a dynamic character that has inner traits reshaped, world views rearranged, feelings revolutionized. This is the difference between static and dynamic characters.
In one sense Okonkwo can be said to be a static character as he is as violent at the end as at the beginning; he is as unable to put language communication (with his explosive stammer) before physical action at the end as at the beginning; he is as unable to balance the female and male harmonies within himself at the end as at the beginning. This inability to change his behavior and emotions would establish him as a static character.
On the other hand, it can be argued that though he seems to be a static character because of this characterization I've described, he is in fact a dynamic character because he recognizes the failure of his tendency for violence over communication; he recognizes his failure to harmonize the female and male and that he needs to do so; he recognizes that his ultimate behavior failures reveal an ultimate internal failure; he recognizes the only relief from his failure is to remove himself from his village forever. This marks this story as a tragedy with the dynamic character's final dynamic realization leading to his death.
Perhaps down in his heart Okonkwo was not a cruel man. but his whole life was dominated by fear, the fear of failure and of weakness. It was deeper and more intimate than the fear of evil ....
A round character differs from a flat character in terms of (1) full-blown detail, (2) believability and (3) 3-dimensionality of the character. As in Jane Austen's work, it is not always a plethora of descriptive detail that creates roundness, indeed, in contrast, many minutely detailed characters are 2-dimensional as in The Awakening. Okonkwo is a round character because his inner and outer traits, his outer behavior and psychological motivations are expressly established.