начальником

начальником

"Начальником" means "boss" or "superior."

In this sentence, 'начальником' is used in the instrumental case to describe the role or capacity to which someone has been appointed.

Он был назначен начальником отдела.

He was appointed as the head of the department.

Here, 'начальником' is implied as 'начальника', indicating the genitive case to describe possession or roles indirectly.

Я работаю под руководством нового начальника.

I work under the guidance of the new chief.

In this usage, 'начальником' implies an instrumental case to denote whom the action of discussing is performed with.

Эта проблема обсуждалась с начальником производственного отдела.

This issue was discussed with the head of the production department.