The word accompanist, this is similar to the other two, which you can read on the pages of this book - conductor and choirmaster also consists of two words: the concert and master (German meister). Is it two values. In the orchestra, so called the best musicians of any group orchestra, which seemed to lead members of this group. If the symphonic work meets a solo episode for any tool, it takes it as an accompanist.
The leader of the main group Symphony orchestra - groups of the first violins is the concertmaster of the entire orchestra. This situation is very responsible and honorable. Accompanist - first assistant conductor with his right hand. Usually, when after the execution of any works to the conductor of the audience applauding, he is sharing his success with the whole orchestra, refers to the leader separately, shakes his hand, thanks for the help. There are cases when the concertmaster of the orchestra even replaces a sick conductor at the control panel.
And the leader is called a pianist who works with students violinists, vocalists, cellists and so on, Such concertmaster assistant teacher guides them, helps them to learn their parts, find the correct interpretation of the work.
A somewhat different role from pianists who accompany singers and instrumentalists - masters of their craft. Here they act as equal members of a single ensemble.