A word that happends to have a very different denotation and connotation. (In other words, a word that has a "definate
definition" but a different "feel" to it.)
Anyway, unadulterated's true
definition basically means "to be not diluted" or "pure."
However it is not always perceived that way, because of the negative contexts that it is
used in.
For example, (1) movies that are R-rated or worse and often have no censorship are considered "unadulterated" bc said movies are not "blocked/filtered/diluted" by the censors. The disgusting movies are considered "unadulterated," "pure," and/or "pure unadulterated fun." Thus, the word "unadulterated" becomes
associated with dirty movies and/or dirty things.
Similarly, (2) the term "unadulterated jealousy"
technically means "pure jealousy" and/or "just jealousy." However the term "feels" like: extreme jealousy, jealousy-without-restraint, and/or unhinged jealousy.
Because of the often
repetitive use of "unadulterated" in negative contexts (especially in slang and/or common spoken language), it starts-to-sound-like a bad word. The word "unadulterated" grows a negative connotation! The word no longer has a "pure" nor "NOT-diluted" feel to it.
(The word has a neutral denotation but a negative connotation.) The word has a new definition to it: bad, tainted, without restraint, dirty, unhinged.