This is the 3632nd most frequent Japanese word.
霧
Fog.
Here, '霧' refers to the natural phenomenon of fog, described in a literal context.
霧が濃くて前が見えない。
The fog is thick, and I cannot see ahead.
'霧' is used metaphorically here to describe a situation where clarity is lacking, similar to being obscured by fog.
その事件の真相はまだ霧の中だ。
The truth of the incident is still unclear.
In this sentence, '霧' again refers to a literal natural mist, this time emphasizing its transient and clearing quality.