幽す[yuusu] to confine to a room
幽闇[yuuan] gloom
幽雅[yuuga] refinement
幽界[yuukai] hades
幽閑[yuukan] quiet and secluded

幽鬼[yuuki] ghost
幽客[yuukaku] orchid
幽居[yuukyo] hermitage
幽境[yuukyou] solitude
幽契[yuukei] secret promise made to the gods

陰鬱[inutsu] gloom
鬱積[usseki] accumulation (e.g. of emotions, grievances, etc.)
抗鬱[kouutsu] antidepressant
鬱を散じる[utsuwosanjiru] to chase one's gloom away
鬱陶しい[uttoushii] gloomy (e.g. mood)

鬱病[utsubyou] melancholia
躁鬱[souutsu] manic-depressive (bipolar)
躁鬱病[souutsubyou] manic depression
鬱血[ukketsu] blood congestion
鬱蒼[ussou] thick