used to emphasize that a belief, feeling, opinion etc is very strong, important, or sincere:
Her lies hurt my father deeply.
She is deeply upset.
He loves her deeply.
Teachers are deeply divided on this issue.
deeply held religious beliefs
in a serious, careful way:
Most doctors think deeply about what their patients want.
a long way into something
John kept sinking more deeply into the mud.
to take a large breath of air into your lungs
to be in a deep sleep, from which it is hard to wake up