A fretsaw is a small saw with a very thin, narrow blade, used to cut curves and open patterns in thin wood — and sometimes in soft metal or plastic. The blade can be taken off and passed through a starter hole, so you can cut a shape inside a piece without coming in from the edge. Craftspeople use it for decorative work: tiny windows in a model, a name cut from a board, the open patterns people call fretwork. It is a workshop word, not an everyday one. Though actually, shops and speakers often mix fretsaw, coping saw, and even jigsaw; a teacher may keep them apart, but a hardware-store conversation may not. The fret here is the old word for ornamental cutting, not the worry word.

線鋸（鋸薄木、鏤出花紋用的細鋸）