Definitions of faithful:

• noun:   any loyal and steadfast following
• noun:   a group of people who adhere to a common faith and habitually attend a given church
• adjective:   steadfast in affection or allegiance

  Example: "Years of faithful service"

• adjective:   not having sexual relations with anyone except your husband or wife, or your boyfriend or girlfriend

  Example: "He remained faithful to his wife"

• adjective:   marked by fidelity to an original

  Example: "A faithful copy of the portrait"