Is y at the end of muddy derivational

The suffix in the word muddy is -y, which is an adjective-forming suffix usually added to nouns and verbs. The root word in muddy is mud.

'Inflectional morphemes' are ones that don't change the part of speech of a word, for instance, the plural suffix -s or the past tense marker -ed:

• bag → bags (both are nouns)
• want → wants, wanted (all of them are verbs)

'Derivational morphemes' on the other hand are ones that do change the part of speech of a word. For example, suffixes like -y, -ise/-ize etc:

• mud (noun) → muddy (adj)
• standard (noun or adj) → standardise (verb)