The phrase "scare daylights out of" is an idiom that means to frighten someone severely. Some synonyms to replace this phrase include, but are not limited to: petrify, spook, terrify, intimidate, startle, shock, and alarm. Each of these words carries a similar connotation of instilling fear or apprehension in someone. Additionally, other phrases that can be used to convey a similar meaning to "scare daylights out of" include "give someone a fright," "make one's blood run cold," and "send shivers down one's spine." All of these phrases can be used to describe a situation where someone is scared or frightened in an intense way.