Siri not responding verbally all the time.

I use Siri all the time for school to find the definitions of new words. But recently I have found some words that does not cause her to verbally respond back. For example, I can ask her to define the word “dirt” but she will not answer me back verbally. She answers in text form but not verbally. Then I can say define the word “yellow” and she verbally responds by saying the definitions. It’s really frustrating for me anyways and I’m wondering if I’m alone with this problem or does someone else have it? Also is there a solution?