This is the 3991st most frequent French word.
brouillard
Fog.
In this sentence, 'brouillard' refers to a weather condition where water droplets form a thick mist near the ground, obstructing visibility.
Le brouillard était si dense ce matin que l'on ne voyait presque rien.
The fog was so dense this morning that one could hardly see anything.
Here, 'brouillard' is used metaphorically to signify confusion or a lack of clarity in one's thoughts.
Un brouillard mental peut rendre difficile la concentration lors d'une longue journée.
A mental fog can make concentrating during a long day difficult.
In this context, 'brouillard' again refers to the atmospheric phenomenon of fog that reduces visibility and requires safety measures.