As a Noun:
1. Things or facts which are known by everybody and not special in any way. English = common knowledge.
As a Verb or Adjective:
1. To be ordinary and not special in any way. English = (be) common.
2. To be very ordinary and so familiar and well-known that it has become uninteresting and boring. Idiomatic English = (be) old hat.
3. To know or recognise something because you have seen, heard, or experienced it before many times; for an experience to be the same as your past experiences and, consequently, to be of little interest or to be not surprising. English = (be) used to.
1. Used alone to tell your addressee that what you have just been told is not special in any way. Indeed, it is uninteresting and boring. English = 'So what! I've heard that a million times.'