what about common sense ?
the word “blood” and the word “libel”
combine them with the definition from each word.
You have made it past the part of your education where you learn how phrases can have meanings distinct from the meaning of the words used in those phrases, right?
If not, at least it would explain your lack of understanding of the difficulty of the use of the phrase “blood libel”.
On the other hand, I think you do understand, because otherwise you wouldn’t suggest that the dictionary definition of “blood” makes the phrase “blood libel” common sense. It’s the interpretation of blood as a metaphor for killing that makes this make sense. Like the phrase “blood on his hands”.
Which is a good example of how a phrase means more than the words. It’s not that a person’s hands are coated in blood, it’s the REASON they are coated in blood that is implied by the phrase.