A cutting tool with a toothed blade, used for woodworking and similar tasks. The cross-reference to のこぎり indicates it is a synonym or near-synonym, but ソー is a modern loanword often used in compound terms or specific contexts.
See also: 鋸
Cut the wood with an electric saw.
Be careful with the chainsaw because it's dangerous.
musical saw
Borrowed from English 'saw'.