coping saw 
noun
A saw with a very narrow blade stretched across a D-shaped frame, used for cutting curves in wood.A coping saw has a c-shaped frame and a handle, which is turned to tighten a thin flexible blade....
- Generally, use a handsaw or a circular saw to cut straight lines, a coping saw or a portable jigsaw to cut irregular lines.
- These cuts can be easily made with a miter saw, and excess wood can be cut away with a coping saw.
Origin
1920s: coping from cope2, used to describe likeness to a vault, arch, canopy, etc..