Expensive or requiring sacrifice.
This is a medium difficulty word that appears on the SAT. When you encounter "Costly" in SAT reading passages, remember that it means "Expensive or requiring sacrifice.". Pay attention to the context clues around this word to understand its precise meaning in the passage.
To master this word, try using it in your own sentences and practice identifying it in SAT practice passages. Understanding vocabulary in context is crucial for the SAT Reading section.