This is the 8472nd most frequent Catalan word.
dissimulen
"Dissimulen" means "they pretend" or "they hide/disguise" in English.
In this sentence, 'dissimulen' refers to the act of hiding or concealing the mess.
Els nens dissimulen el desordre de l'habitació quan venen els seus pares.
The children disguise the mess in the room when their parents come.
Here, 'dissimulen' is used to describe hiding emotions or feelings.
Tot i que actuen contents, en realitat dissimulen la seva tristesa.
Although they act happy, in reality, they conceal their sadness.
In this case, 'dissimulen' refers to masking or camouflaging nervous emotions.