What is the term for the relationship between two words when they have similar but not identical pronunciation? For example the words "cheat" and "sheet", "core" and "sour", "think" and "thank", "tough" and "cuff" sound very similar. I am not talking in the context of poetry but to clarify these words may be used in poetry.
PS: The only thing I care about is how two words sound in ear. I don't care if there is a category to which a pair of words mentioned above belongs or if such a category does not exist: "core" is similar to "sour" because a human can understand it and can understand "core" is far from "black" without providing any reason.