The word عقيدة (Islamic Creed) is derived from the root word عقد which means ‘to tie’, ‘to fasten’. However in the context of ‘Islamic creed’, it refers to those matters which are believed in with certainty and conviction. Abu Hafs Siraj al-Din al-Ghaznawi (773 AH) writes in his commentary on al-Aqidah al-Tahawiya:
“The word عقيدة is in the form of فعيلة which has the meaning of مفعول i.e. belief which has been firmly held by the heart”.
العقيدة ((فعيلة)) بمعني ((المفعول))، أي: المعقودة التي عقد عليها القلب
(شرح العقيدة الطحاوية لابي حفص سراج الدين الغزنوي الهندي، ص25،