squinch: a small arch built across the interior angle of two walls (usually to support a spire)
arch: (architecture) a masonry construction (usually curved) for spanning an opening and supporting the weight above it
tantra: doctrine of enlightenment as the realization of the oneness of one's self and the visible world; combines elements of Hinduism and paganism including magical and mystical elements like mantras and mudras and erotic rites; especially influential in Tibet