Final answer:
Synonyms and antonyms are words that have similar and opposite meanings, respectively. It is important to understand them to improve vocabulary and comprehension skills in English.
Step-by-step explanation:
The subject of this question is English and the grade level is High School. Synonyms are words that have similar meanings, while antonyms are words that have opposite meanings. In this case, the synonyms provided are stern, rigorous, tough, urgent, and imperative, which all convey a sense of seriousness or urgency. The antonyms are lenient, mild, lax, and permissive, which convey a sense of leniency or relaxedness. Understanding the meanings of synonyms and antonyms is important for improving vocabulary and comprehension skills in English.