1) Become covered with clouds 2) Become dark and gloomy 3) Cloud over 4) Cloud up 5) Darken 6) Make obscure or unclear 7) Obscure 8) To cast sorrow or gloom over 9) To darken 
• (v. t.) To cover or overspread with clouds; to becloud; to overcast.
O`ver·cloud' transitive verb To cover or overspread with clouds; to becloud; to overcast. 
[v] - become covered with clouds
to overspread with or as if with clouds: a summer storm that briefly overclouds the sun; to overcloud one's pleasure with solemn thoughts. · to darken; obscure; make gloomy: a childhood that was overclouded by the loss of his parents.