Can one word be an adjective and adverb?

Yes, absolutely! Many words in English can function as both adjectives and adverbs. These are called adjectives of manner, and they typically describe how something is done or how something happens.

Examples:

* Fast:

* Adjective: "He drove a fast car." (Describing the car)

* Adverb: "He drove the car fast." (Describing how he drove)

* Slow:

* Adjective: "The snail made slow progress." (Describing the snail's progress)

* Adverb: "The snail moved slow." (Describing how the snail moved)

* Hard:

* Adjective: "He had a hard time." (Describing the time)

* Adverb: "He worked hard." (Describing how he worked)

* Loud:

* Adjective: "The music was loud." (Describing the music)

* Adverb: "She spoke loud." (Describing how she spoke)

Keep in mind that sometimes, the word needs a slight change to function as an adverb. For example, "good" is an adjective, but "well" is its adverbial form.