What is the old movie where husband tries to kill wife but it thwarted by a ghost?

The movie you're thinking of is likely "The Ghost and Mrs. Muir" (1968). In this romantic fantasy film, a widow named Lucy Muir moves into a seaside cottage haunted by the ghost of a sea captain, played by Rex Harrison. While the primary plot revolves around their developing relationship, there are elements involving danger and threats from the living, particularly with Lucy's scheming husband. The ghost ultimately protects her, adding a supernatural twist to the narrative.