Answer:
generalization
Step-by-step explanation:
Generalization occurs when the meaning of a word changes from specific to general, or it extends to include a relevant concept. As a result, since the noun noble means aristocrat, which refers to a member of the highest class, the term is assumed as an adjective to describe someone with refined individual qualities or high moral principles.
The rest of the alternatives are incorrect because amelioration is an improvement in the meaning of a word; pejoration happens when a word is downgraded in meaning of status; and specialization refers to a meaning change from general to specific.