punishment / retribution
Masculine verbal noun (maṣdar) of عَاقَبَ (Form III = to punish). Related: عَقِبَ (to follow/succeed), عَاقِبَةٌ (consequence/outcome), عُقْبَى (final result).
The phrase 'shadīdu al-ʿiqāb' (severe in punishment) is often balanced in the same verse or context with 'ghafūrun raḥīm' (forgiving, merciful), maintaining the Quranic balance of hope and fear.