Judoka (practitioner)
A practitioner of Judo is known as a Judoka (柔道家, jūdōka?, Judo practitioner), though traditionally only those of 4th dan or higher were called "Judoka". The suffix -ka (家?), when added to a noun, means a person with expertise or special knowledge on that subject. Other practitioners below the rank of 4th dan used to be called kenkyu-sei (研究生?, trainees). The modern meaning of "Judoka" in English refers to a Judo practitioner of any level of expertise.
A Judo teacher is called sensei (先生?). The word sensei comes from sen or saki (before) and sei (life) – i.e. one who has preceded you. In Western dojo, it is common to call any instructor of dan grade sensei. Traditionally, that title was reserved for instructors of 4th dan and above.
Read more about this topic: Judo