What part of speech is the word serious?

The word "serious" can be several parts of speech depending on its use in a sentence:

* Adjective: Describing a noun. Example: "She has a serious problem."

* Noun: Referring to the quality of being serious. Example: "His expression was full of seriousness."

* Adverb: Modifying a verb, adjective, or another adverb. Example: "He was seriously injured."

To determine the part of speech, look at the context of the word in the sentence.