The question asks us to find the word that is opposite in meaning to the underlined word "serious" in the sentence, "He is very serious by temperament." We need to understand the meaning of "serious" in this context and then examine the given options to find its antonym.

In the sentence, "serious by temperament" means someone who is thoughtful, not easily amused, perhaps solemn, and who takes things with gravity rather than lightness. It describes a personality trait.

Analyzing the Antonym Options for Serious

Let's look at the meanings of the given options:

• grave: This word means serious, solemn, or of great importance. This is a synonym for "serious," not an antonym.
• trivial: This word means of little value or importance. In the context of temperament, someone who is "trivial" might focus on insignificant matters or approach life in a lighthearted or superficial way, which is contrary to being serious.
• sober: This word can mean not drunk, but it also means serious, sensible, or solemn. This is similar in meaning to "serious," making it a synonym or related term, not an antonym.
• stupid: This word means lacking intelligence or common sense. This is not related to the concept of being serious or lighthearted by temperament.

Comparing the options, "trivial" is the word that best represents the opposite of being serious, especially when describing temperament. While "serious" implies depth, importance, and gravity, "trivial" implies a lack of depth, importance, and seriousness.

Therefore, the most appropriate antonym for "serious" in the context of temperament among the given options is "trivial".

Meaning of Serious

The word "serious" can have several meanings depending on the context. Here are a few common ones:

1. Important: Requiring careful consideration or attention; not trivial. (e.g., a serious problem)
2. Solemn or thoughtful: Not cheerful or smiling; having or showing deep thought. (e.g., He looked serious)
3. Sincere: Not joking or intended to be humorous. (e.g., Are you serious?)
4. Significant or severe: Of considerable amount or intensity. (e.g., a serious injury)

In the phrase "serious by temperament," meaning 2 (solemn or thoughtful) and a general sense of taking things with importance (meaning 1) are most relevant. The opposite would be someone who is lighthearted, focuses on unimportant things, or is not solemn.

Based on the analysis, "trivial" is the clear opposite of "serious" in the context of temperament.

Revision Table: Key Vocabulary

Additional Information: Understanding Antonyms

Antonyms are words that have opposite meanings. Understanding antonyms is a key part of building vocabulary. Sometimes, a word can have more than one antonym depending on the specific shade of meaning being used. For example, the opposite of "hot" could be "cold," "cool," or "freezing," depending on the context. Similarly, the opposite of "serious" when referring to a situation might be "minor" or "insignificant," while the opposite of "serious" when referring to a person's attitude or temperament is often "lighthearted," "joking," or, as in this case, "trivial" in the sense of not focusing on important matters.