凹ます[hekomasu] to dent
凹ませる[hekomaseru] to dent
凹まる[kubomaru] to be low (as a hollow)
凹む[hekomu] to be dented
凹める[kubomeru] to hollow out

凹レンズ[ourenzu] concave lens
凹眼[ougan] cavernous eyes
凹眼鏡[ougankyou] concave glasses
凹型[ougata] concavity

窪溜まり[kubotamari] hollow
窪み[hekomi] hollow
窪む[kubomu] to cave in
笑窪[ekubo] dimple

窪地[kubochi] pit
盆の窪[bonnokubo] hollow at nape of the neck
落ち窪む[ochikubomu] to sink in
片笑窪[kataekubo] dimple on one cheek