The ornamental design of a glasswindow with an arc-shaped muntin, as shown and described.
FIG. 1 illustrates a window with an arc-shaped muntin, such as could be placed on the left side of a room or wall.
FIG. 2 illustrates a second embodiment of a window with an arc-shaped muntin, such as could be placed on the right side of a room or wall; and,
FIG. 3 illustrates left and right widows with arc-shaped muntins positioned on an exterior wall, such that the arc-shaped muntins together trace a portion of a two-centered (gothic) arch or a one-centered (semi-circular) arch.
The broken lines in the drawings depict environmental subject matter only and form no part of the claimed design.