Synonyms of "scariness" can be "frightfulness", "terrifying quality", "alarm", and "awe-inspiring horror".
"Frightfulness" emphasizes the state of being full of fright or causing great fear. For example, "The frightfulness of the haunted house sent shivers down our spines."
"Terrifying quality" refers to the characteristic of being extremely terrifying. It describes the aspect that causes terror. For instance, "The movie had a terrifying quality that kept the audience on the edge of their seats."
"Alarm" can also be used in the context of scariness as it implies a sense of sudden fear or apprehension. "The strange noise in the middle of the night caused alarm and made us wonder what was happening."
"Awe-inspiring horror" combines the elements of awe and horror. It suggests that something is so terrifying that it also elicits a sense of wonder or amazement. "The sight of the massive tornado was an awe-inspiring horror."
These synonyms all capture different aspects of scariness, from the pure feeling of fright to the combination of fear and wonder.