This is the 18362nd most frequent Russian word.
экономистом
"Economist" – a specialist in economics.
The word "экономистом" here is used as an instrumental case noun denoting the profession of the subject, explaining his role or function.
Мой брат работает экономистом в крупной компании.
My brother works as an economist in a large company.
In this instance, "экономистом" serves as the instrumental case of the noun to express a desired role or professional identity that the subject aims to achieve.
Она мечтает стать хорошим экономистом.
She dreams of becoming a good economist.
Here, "экономистом" is used in the instrumental case to describe the transformation or acquisition of a professional status after completing education, indicating the resultant profession.