悪循環[akujunkan] vicious circle
一環[ikkan] link (e.g. a part of a larger plan)
印環[inkan] signet ring (in medical contexts, e.g. signet ring cell)
円環[enkan] circle
花環[hanawa] wreath

環境[kankyou] environment
環境グループ[kankyouguruupu] environmental group
環境事業[kankyoujigyou] environmental business
環境庁[kankyouchou] Environment Agency
環境庁長官[kankyouchouchoukan] Director General of Environment Agency

暗礁[anshou] reef
環礁[kanshou] atoll
岩礁[ganshou] reef
サンゴ礁[sangoshou] coral reef
離礁[rishou] refloat

堡礁[hoshou] barrier reef
坐礁[zashou] running aground
漁礁[gyoshou] fish reef
暗礁に乗り上げる[anshouninoriageru] to run aground