I think there's a word for it, but I don't know what it is. I think there's a word for it, because it happens often. Like for example, using cubicle instead of cuticle, because both words sound similar.
For example:
Using cubicle to mean cuticle is an example of ___.
That would be a malapropism, named for a character in a comic play - though it is likely that her name was chosen as reference to malapropos, a word deriving from French and meaning, as an adjective, inopportune or inappropriate, or as an adjective meaning in an inopportune or inappropriate manner.
Malapropism or a malaprop (specific instance of malapropism) is the correct answer to this question. But "to conflate" might also work in this case since you are describing someone who mistakenly says "cubicle" when they really mean "cuticle", which is essentially, an example of conflation.
