In the following question, out of the four alternatives, select the alternative which is the best one-word substitute for the given group of words: "A person or thing that is likely to cause harm".

Introduction / Context:
This vocabulary question asks for a one word substitute for the descriptive phrase "a person or thing that is likely to cause harm". One word substitutions are commonly tested in competitive exams to check whether learners can compress a descriptive definition into a single precise term. The challenge lies in knowing both the exact meaning of the target definition and the meanings of the candidate words.

Given Data / Assumptions:

• Definition: "A person or thing that is likely to cause harm".
• Options: "Menace", "Cordial", "Festal", "Blithe".
• We must choose the word that captures the idea of potential danger or harmfulness.

Concept / Approach:
The word "menace" means a person or thing that is a threat or likely to cause harm. It is used both for people and for situations that can be dangerous or troublesome. The other options have positive, friendly, or celebratory meanings and therefore do not fit the definition. By matching the central idea of "likely to cause harm" with the correct word, we can confidently select "menace".

Step-by-Step Solution:
Step 1: Focus on the key idea in the definition: the person or thing is "likely to cause harm". Step 2: Examine "Menace". It means a threat or danger, something that can cause harm or trouble, which matches the definition well. Step 3: Examine "Cordial". This means warm and friendly, which is the opposite of dangerous or harmful. Step 4: Examine "Festal". This relates to a festival or celebration and suggests joy, not harm. Step 5: Examine "Blithe". This means carefree or joyous, again far from the idea of causing harm. Step 6: Conclude that "Menace" is the only word that fits the given description.

Verification / Alternative check:
Consider typical sentences. One might say, "Drunk driving is a menace on the road" or "The gang was a menace to the neighbourhood." In each case, the word clearly expresses that the person, group, or activity is likely to cause harm. In contrast, words like "cordial" and "blithe" usually appear in positive settings such as cordial relations or blithe spirit, which do not suggest danger at all. This comparison confirms the choice of "menace".

Why Other Options Are Wrong:

• Menace: Correct answer, as it directly denotes something or someone that is a threat or likely to cause harm.
• Cordial: Means warm and friendly, which is incompatible with the notion of causing harm.
• Festal: Connected to festivities and celebrations, not to danger or threat.
• Blithe: Refers to a carefree, cheerful attitude, again opposite in tone to menace.

Common Pitfalls:
One risk is that learners may not know the less common words such as "festal" and "blithe" and might try to guess based mainly on sound rather than meaning. Another error is to confuse "menace" with "medicine" or similar sounding words. Building a strong vocabulary through regular reading and making notes of new words can help avoid reliance on pure guesswork in such questions.

Final Answer:
The one word substitute for "a person or thing that is likely to cause harm" is Menace.