From the Etihad Newsletter.
Terms and Conditions copied from website
•American Express Card Members can receive up to 10% off when booking a flight with Etihad.
•The discount is only valid on the following booking classes: 5% discount on all Saver and Value Fares and 10% discount on all Freedom Fares.
•Card Member must book and travel by 31 December 2014.
•Payment must be with an American Express Card and bookings must be made on etihad.com/amexoffer.
•Flights and fare types are subject to availability at the time of booking.
•The discount only applies to flights marketed and operated by Etihad, which is only applied to the base fare and not on taxes or additional charges.
•From time to time, Economy Class fares categorized as Breaking Deals may be available for sale. Discount will not apply to these Breaking Deal fares, but will be bookable through etihad.com/amexoffer.
•Discount is not applicable for child or infant fares.
•Changes and cancellations are subject to charges and fees as per published fare rules.
•All changes must be made with Etihad via etihad.com or Etihad Contact Centres.
•Discount is available on Economy, Business and First Class fares only.
I tested some discount Economy fares through the link and without using the link and they are slightly cheaper with the Amex offer.
Direct URL
Incorrect url or under maintainance