This is the 7656th most frequent Russian word.
жумашев
The word "жумашев" is not a standard Russian word; it appears to be a proper noun, such as a surname.
Here, 'Жумашев' is used as a proper noun - a personal name referring to an individual.
Жумашев был моим преподавателем истории в прошлом году.
Jumashov was my history teacher last year.
In this sentence, 'Жумашевым' is the instrumental case form of the proper noun 'Жумашев', indicating companionship or means.
Мы часто обсуждали с Жумашевым интересные исторические события.
We often discussed interesting historical events with Jumashov.
Here, 'Жумашева' is in the accusative case, showing that 'Жумашев' is the direct object of the thanking action.