faithfulness

Concise Oxford English Dictionary © 2008 Oxford University Press:
faithful/ˈfeɪθfl/

▶adjective

• 1 remaining loyal and steadfast.

  ■ remaining sexually loyal to a lover or spouse.

• 2 true to the facts or the original.

▶noun (the faithful) those who are faithful to a particular religion or political party.

– derivatives
faithfulness noun.