IPA: /pəˈrɛnθɪkli/
KK: /pɛrənˈθɛtɪkli/
In a way that is not the main point, often used to add extra information or a comment.
She mentioned, parenthetically, that she would be late to the meeting.
Parenthetically → It is formed from "parenthesis" (from Greek "parenthesis", meaning insertion or to place beside) and the suffix "-ally" (meaning in a manner of). The word "parenthetically" means in a manner that involves an insertion or side note.
Think of a 'parenthesis' as an insertion of extra information, and remember that 'parenthetically' means doing something in a way that includes that extra note.