Window sill for covering a parapet underneath a window or a door, comprising - a parapet cover element, which along its longitudinal extension comprises front faces interspaced from each other and an underside and an upper side facing away therefrom, - at least one terminating part which is connected to the parapet cover element in the region of a front face, - at least one end piece, which has a substantially U-shaped profile along the longitudinal extension of the parapet cover element, is open towards the latter and extends at least over a part of the depth of the parapet cover element, said end piece having first and second limbs (22, 23) which are oriented parallel to the parapet cover element and interspaced from one another in a direction perpendicular with respect to the longitudinal extension of the parapet cover element, said limbs (22, 23) being interconnected by means of a base web, and on the second limb arranged adjacent to the underside of the parapet cover element, on the end thereof facing away from the base web, a first support web is arranged, which protrudes towards the underside of the parapet cover element, - and the second limb of the end piece arranged adjacent to the underside of the parapet cover element overhangs with a subsection thereof the terminating part along the longitudinal extension of the parapet cover element, - wherein an expansion joint is formed between an inner face of the base web of the end piece and the terminating part, characterized in that - a seal element is arranged between the underside of the parapet cover element and the end piece, - and that the seal element is arranged in the subsection of the second limb of the end piece overhanging the terminating part next to the terminating part and extending between the underside of the parapet cover element and the second limb, - wherein the seal element is connected, in particular bonded, both to the underside of the parapet cover element and to the subsection of the second limb of the end piece, - and as a result, a channel is formed in the region of the underside of the parapet cover element by the seal element and the terminating part arranged on the parapet cover element, said channel extending at least over the depth extension of the end piece in the direction of the parapet depth of the parapet to be covered. - a parapet cover element, which along its longitudinal extension comprises front faces interspaced from each other and an underside and an upper side facing away therefrom, - at least one terminating part which is connected to the parapet cover element in the region of a front face, - at least one end piece, which has a substantially U-shaped profile along the longitudinal extension of the parapet cover element, is open towards the latter and extends at least over a part of the depth of the parapet cover element, said end piece having first and second limbs (22, 23) which are oriented parallel to the parapet cover element and interspaced from one another in a direction perpendicular with respect to the longitudinal extension of the parapet cover element, said limbs (22, 23) being interconnected by means of a base web, and on the second limb arranged adjacent to the underside of the parapet cover element, on the end thereof facing away from the base web, a first support web is arranged, which protrudes towards the underside of the parapet cover element, - and the second limb of the end piece arranged adjacent to the underside of the parapet cover element overhangs with a subsection thereof the terminating part along the longitudinal extension of the parapet cover element, - wherein an expansion joint is formed between an inner face of the base web of the end piece and the terminating part, - a seal element is arranged between the underside of the parapet cover element and the end piece, - and that the seal element is arranged in the subsection of the second limb of the end piece overhanging the terminating part next to the terminating part and extending between the underside of the parapet cover element and the second limb, - wherein the seal element is connected, in particular bonded, both to the underside of the parapet cover element and to the subsection of the second limb of the end piece, - and as a result, a channel is formed in the region of the underside of the parapet cover element by the seal element and the terminating part arranged on the parapet cover element, said channel extending at least over the depth extension of the end piece in the direction of the parapet depth of the parapet to be covered.