use the word "impregnable in a sentence.

Our campus is an impregnable fortress.

http://www.answers.com/impregnable

Sure! Here's an example sentence using the word "impregnable":

"The fortress was built with thick stone walls and extensive security measures, making it practically impregnable to any external attack."

If you're interested in learning how to use vocabulary words effectively, here's a tip: It's helpful to try using new words in different contexts or situations to fully understand their meaning and usage. This could involve imagining or describing scenarios where the word would be applicable, or even creating short stories or conversations using the word. Additionally, reading extensively and paying attention to how words are used in different contexts can also enhance your understanding and usage of vocabulary words.