Which of the following describes a morpheme added to a root word?

An affix is defined as a morpheme that is attached to a root word to modify its meaning or create a new word. This can include prefixes, which are added to the beginning of a root, and suffixes, which are added to the end. For instance, in the word "unhappiness," "un-" is a prefix that alters the meaning of "happy," while "-ness" is a suffix that changes the adjective "happy" into a noun.

In this context, the other options do not represent morphemes added to root words. A compound refers to a word formed from two or more root words coming together, like "notebook" (from "note" and "book"). A pronoun is a word that takes the place of a noun, such as "he," "she," or "it," and does not modify a root word. A conjunction is a part of speech used to connect clauses or sentences, such as "and," "but," or "or," and likewise does not pertain to the modification of root words through morphemes. Thus, the term that correctly describes a morpheme added to a root word is an affix.