noun
office; workroom
A formal term for a room where official duties or business is conducted, such as an executive's office or a government official's office. Often used in official contexts.
社長は執務室で来客と会談した。
The company president met with a visitor in his office.
大臣の執務室には重要な書類が保管されている
Important documents are kept in the minister's office.
オフィス is a common loanword for a workplace or office in a broad sense, whereas 執務室 is a more formal, specific term for an official's workroom.
Compound of 執務 (shitsumu, 'performance of duties') + 室 (shitsu, 'room'). The term is straightforwardly derived from its components.