Still waiting for your definition of the priesthood in general, but in the meantime this is a good scripture in the D&C for some context to your question.
11 Again I say unto you, that it shall not be given to any one to go forth to preach my gospel, or to build up my church, except he be ordained by some one who has authority, and it is known to the church that he has authority and has been regularly ordained by the heads of the church.