This is the 3038th most frequent Catalan word.
llindar
Threshold.
Here, 'llindar' is used literally to refer to the physical threshold or limit, specifically the doorway threshold.
El llindar de la porta estava decorat amb flors.
The threshold of the door was decorated with flowers.
In this context, 'llindar' is used metaphorically to indicate a limit or critical point that triggers a significant change or event; here it is the critical temperature.
Estem a punt d'assolir el llindar crític de temperatura.
We are about to reach the critical temperature threshold.
This use of 'llindar' conveys an abstract boundary, signifying the extent to which something can occur before a response or change is elicited; it is used to describe the endurance limit for patience.