This is the 152nd most frequent Hebrew word.
חדש
"חדש" (chadash) means "new" or "month" depending on context.
The word 'חדש' describes something that is new, in this case, the book.
אני קונה ספר חדש.
I am buying a new book.
The word 'חדש' is used to describe the newness of the course, implying it wasn't available before.
באוניברסיטה התחילו קורס חדש.
A new course has started at the university.
Here, 'מחדש' (an adverbial form derived from 'חדש') means 'anew' or 'again', indicating a reoccurrence or fresh start of an emotion or action.