authenticity

Concise Oxford English Dictionary © 2008 Oxford University Press:
authentic/ɔːˈθentɪk/

▶adjective

• 1 of undisputed origin or veracity; genuine.

• 2 Music (of a church mode) containing notes between the principal note or final and the note an octave higher. Compare with plagal.

– derivatives
authentically adverb,
authenticity /ɔːθɛnˈtɪsɪti/ noun.

– origin ME: via OFr. from late L. authenticus, from Gk authentikos ‘principal, genuine’.