Adjectival means relating to adjectives or functioning like an adjective. An adjective is a word that describes a noun, like tall, blue, or interesting. When something is adjectival, it works the same way, adding description or detail to a noun.

Sometimes a word that isn't technically an adjective can do an adjective's job. In the phrase “stone wall,” stone is actually a noun, but it's being used in an adjectival way because it describes what kind of wall we're talking about. In “morning coffee,” morning works adjectivally to tell us when that coffee is drunk.

You might see this word when learning about grammar or sentence structure. A teacher might point out an adjectival phrase like “covered in mud” in the sentence “The dog covered in mud ran through the house.” That whole phrase describes which dog, just like a single adjective would.

Understanding adjectival words and phrases helps you see how language is flexible. Writers don't just rely on pure adjectives like muddy. They can turn all sorts of words and phrases into adjectival elements that make their sentences more specific and interesting. When you write “birthday present” instead of just “present,” you're using birthday adjectivally to tell your reader exactly what kind of present you mean.