The phrase "scare stiff" is an idiom that refers to the act of making someone extremely frightened, causing them to freeze or become paralyzed with fear. Some antonyms or opposite terms for "scare stiff" could include "reassure," "calm," "comfort," "soothe," "lull," "pacify," "relax," "placate," or "sedate." These words all imply a sense of easing someone's anxiety or fears rather than causing them discomfort or stress. Using these opposite terms can help to convey a different and more positive tone, making the conversation more effective and productive.