Which term refers to a situation where a word takes on a worse connotative meaning?

The term that describes a situation where a word takes on a worse connotative meaning is "deterioration." This concept signifies a shift in the meaning of a word where it begins to carry negative or less favorable associations over time. For instance, the word "silly" originally meant "happy" or "fortunate," but its meaning has deteriorated to imply foolishness or lack of good sense.

In contrast, other options like "elevation" would refer to a positive shift in connotation, where a word takes on a better or more favorable meaning. "Assimilation" pertains to the process by which a word or sound becomes similar to what surrounds it, which does not directly relate to changes in connotation. "Sound addition" is not a standard term in this context and does not align with the concept of changing meanings. Therefore, "deterioration" is the most accurate choice reflecting the negative shift in connotation.