What is a derivational affix?

A derivational affix is indeed a prefix or suffix that changes a word's meaning. This type of affix helps in creating new words by altering the base or root word significantly. For example, adding the prefix "un-" to the word "happy" forms "unhappy," which changes the meaning of the original word. Similarly, adding the suffix "-ness" to "happy" creates "happiness," shifting it from an adjective to a noun. Such changes can affect not only the meaning but also the grammatical category of the word, thereby demonstrating the versatility and importance of derivational affixes in language.

The other options presented do not accurately define a derivational affix. For instance, inflectional endings that denote tense are specifically focused on changing grammatical forms rather than the core meaning of the word. A letter added to a consonant cluster is more relevant to phonics than morphology, and a phoneme within a syllable pertains to the sounds of language rather than word formation. Thus, the choice that identifies a derivational affix as a change-maker in meaning is the most accurate representation.