verb.
To be dark, gloomy, and threatening, as clouds; to be covered with dark and threatening clouds, as the sky; to show threatening signs of approach, as a tempest.
verb.
To frown; to look sullen.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
verb.
look angry or sullen, wrinkle one's forehead, as if to signal disapproval
verb.
make lower or quieter
verb.
set lower
Word Usage
"The sun might shine, or the clouds might lour; but nothing could appear to me as it had done the day before."