The answer to this question depends on your personal preference and style sheet requirements. Generally, copyeditor is always written as one word by most style sheets, including the Associated Press Stylebook, the Chicago Manual of Style, and the Modern Language Association. However, some style sheets do allow for the use of two words when referencing the profession, such as "copy editor" instead of "copyeditor."
The best way to determine which style to use is to consult the requirements of your particular style sheet. Have a look at some of the popular style sheets below:
- Associated Press Stylebook: copyeditor
- Chicago Manual of Style: copyeditor
- Modern Language Association: copyeditor
- American Psychological Association: copy editor
Ultimately, it is up to you to decide which usage works best for your particular project.