عُقْبَا

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – عُقْبَا is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

العُقْبَى is the natural state of this definite noun and it remains العُقْبَى even though it is in the genitive case due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it or 3) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

because the third radical in العُقْبَى is a weak letter (و or ي) and weak letters do not show their endings, their endings have to be estimated (deduced by reason)

العُقْبَى loses it’s definite article ال, changing to عُقْبَا due to it being a possessed noun

Requital, Result, Reward, End, Success

To succeed, take the place of, come after, strike on the heel, come at the heel, follow anyone closely

مَعْرِفَةٌمُفْرَدٌمُؤَنَّثٌمَنْصُوْبٌع ق ببَاب سَمِعَعَقِبَ يَعْقَبُفُعْلَىاسْمٌالْاِسْمُ التَّفْضِيْلُ
DefiniteSingularFeminineAccusativeRootConsequenceسPatternNounSuperlative noun
Surah/Below is the 1 verse in the holy Quran containing the accusative nounعُقْبَا
Verse 
13-22
13-24
13-35
13-42
91-15and He fears not the consequences of itوَلَا يَخَافُ عُقْبَاهَا