Words and phrases that tell more about the main verb in a predicate make up the extension of  the verb.
Look at the following sentence:
The thin yellow cat crept silently toward the rabbit.
The complete subject of the sentence is “The thin yellow cat.”
The complete predicate of the sentence is “crept silently toward the rabbit.”
The main verb in the predicate is “crept.” The extension of the verb is “silently toward the rabbit.”
The extension of the verb is the part of the predicate that tells more about the verb. In this example, silently tells how the cat crept, and toward the rabbit tells where or in which direction the cat crept.
