der Arbeitskollege
coworker
A person you work with, usually in the same company or department.
Ich gehe in der Mittagspause oft mit meinen Arbeitskollegen essen.
I often go out to eat with my coworkers during my lunch break.

coworker
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coworker
A person you work with, usually in the same company or department.
Ich gehe in der Mittagspause oft mit meinen Arbeitskollegen essen.
I often go out to eat with my coworkers during my lunch break.

This word is a clear example of a German compound. It is made up of 'die Arbeit' (work), the linking '-s-', and 'der Kollege' (colleague). So it literally means a 'colleague from work.'
Mein Arbeitskollege hat mir bei dem Projekt sehr geholfen.
My coworker helped me a lot with the project.
The base word is 'Kollege' (colleague). The first part 'Arbeits-' specifies what kind of colleague it is. In the same way, you can describe other colleagues, for example 'Studienkollegen' (fellow students) at university.
Ich treffe mich heute Abend mit ein paar ehemaligen Arbeitskollegen.
I'm meeting a few former coworkers this evening.
Common verbs used with 'Arbeitskollege' (coworker) are 'sich gut verstehen mit' (to get along well with), 'zusammenarbeiten mit' (to work together with), or 'sich treffen mit' (to meet up with). The plural form 'Arbeitskollegen' (coworkers) is often used.
Sie versteht sich gut mit ihren neuen Arbeitskollegen.
She gets along well with her new coworkers.
employee
'der Mitarbeiter' and 'der Arbeitskollege' can both mean a person at the workplace. 'Mitarbeiter' describes more the role in a company, public authority, or organization. For example, you say how many employees a business has. 'Arbeitskollege' describes the relationship to a person you work with yourself. Learners may confuse the words because both appear in a work context. A practical rule is: from the company's perspective, someone is a 'Mitarbeiter' (employee); from your own perspective, he is your 'Arbeitskollege' (coworker).

Nach der Besprechung hat Anna mit einem Arbeitskollegen über das Projekt gesprochen.
After the meeting, Anna talked with a coworker about the project.
Der neue Mitarbeiter bekommt heute seinen Schlüssel für das Büro.
The new employee is getting his key to the office today.