Ibram means to - tie a knot to keep something firm, i.e. your Shoelaces. Or the Arabs in the past would tie ropes to the foundation beams of a building, and these knots would keep the beams firm - so the house could be built upon this foundation.
In arabic, there are Nouns, and there are Verbs.
The Noun form is used when someone is firm and committed in their role. I.e. a Mu'min is someone who is committed to Emaan [belief].
Muslims are called 'aladheena aamanoo' - those who say they believe. So they are described in Verb form, because sometimes/temporary they are committed, but sometimes they're not fully committed.
Now going back to the word Ibram, Allah says about the disbelievers;
أَمْ أَبْرَمُوا أَمْرًا فَإِنَّا مُبْرِمُونَ
Have they tied their knot (Verb/temporary Form) in their plan [of disbelief]?
Then surely We [Allah] have tied ourknot/plan (Noun/permanent form) [of sealing/knotting their destiny in the hellfire].
We Learn from this;
The Disbelievers - who have chosen to remain firm on disbelief - have (verb = temporarily) tied their knot to their disbelief, and Allah has tied His knot (noun = permanently - sealed/knotted their destiny for the hellfire].
Why was their decision a verb/temporary and Allah's decision a noun/permanent decision?
On Judgment Day...
Because on Judgment Day - the disbelievers would wish they were Muslims;
رُّبَمَا يَوَدُّ الَّذِينَ كَفَرُوا لَوْ كَانُوا مُسْلِمِينَ
Perhaps those who disbelieve will wish that they had been Muslims.
[al Hijr 15:2]
- on Judgment Day and in Hell - so their verb of wanting to stay on disbelief was temporary, but Allah's decision of punishing them in hellfire is permanent, and forever, ongoing and will not change.