There might be many. You cannot put on some certain until you see the context. However, it maight suggest- Horror scenery, frightening situation, and may be something that is polluted.
water
Chamber, Sorrow, Ghastly, Ebony, Grim
Water is the most rated answer as the word
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Portentous means an action or circumstance has some bearing on the future. It usually has a somewhat dark or negative connotation.
dark water evaporates first
It is a neutral connotation.
Negative connotation
...connotation!
It is a negative connotation.
uneasy is negative connotation
A general connotation for infinity is forever, but because connotation is dependent on the individual reader, the connotation varies.