This is the 8830th most frequent Turkish word.
sis
Mist or fog.
Here, 'sis' refers to the environmental phenomenon of fog, used adjectivally as 'sisli'.
Sabah dışarı çıktığımda hava oldukça sisliydi.
When I went outside in the morning, the weather was quite foggy.
In this sentence, 'sis' directly refers to fog as a noun.
Sis yüzünden görüş mesafesi azaldı.
Due to the fog, the visibility distance decreased.
Here, 'sis' is used metaphorically to describe something dispersing or disappearing like fog.