Delete field's machine-name in Drupal 7

Question

I'm trying to create a new field, but Drupal came up with the well-known error:

The machine-readable name is already in use. It must be unique

I'm sure that the field doesn't exist anymore (I checked the fields' list and it doesn't show up).

I want to use that specific machine name because I already have developed some functions that are using that name.

So I guess the name is still saved in the database, there is a way to delete it without screw everything up?

Answer 1

I have used this answer to manually delete the field from the database and it worked!

Answer 2

Try to clear cache or check if you can find a field with this machine name in reusable fields list.