What part of speech is the word lined?

The word "lined" can be either an adjective or a verb (past participle), depending on its context.

Here are examples:

Adjective:

* "The notebook had lined pages." (Describing the pages)

Verb (past participle):

* "The street was lined with trees." (Describing an action that has been completed)

To determine the part of speech, you need to look at how the word is used in the sentence.