一叢[hitomura] copse
稲叢[inamura] stack of rice straw
叢がる[muragaru] to swarm
叢雨[murasame] passing shower
叢時雨[murashigure] autumn shower

叢書[sousho] series (of publications)
叢生[sousei] dense growth
叢談[soudan] collection of stories
叢氷[souhyou] pack ice
叢立ち[soudachi] standing in a group

暗雲[anun] dark clouds
闇雲[yamikumo] recklessly
いわし雲[iwashigumo] cirro-cumulus
雨雲[amagumo] rain cloud
雲隠れ[kumogakure] disappearance

雲影[unei] cloud shape
雲海[unkai] sea of clouds
雲間[kumoma] rift between clouds
雲形[kumogata] cloud formations