Prefix 'im-' and Antonym Formation

The question asks us to identify the word that does NOT form an antonym (opposite meaning) by simply adding the prefix 'im-'. The prefix 'im-' is often used in English to create a negative or opposite meaning, similar to 'un-' or 'in-'. We need to examine each option to see if 'im-' acts as a negating prefix to a base word.

Impassive: Word Analysis

• The word is impassive.
• The base word here is passive.
• Passive means accepting or allowing what happens or what others do, without active response or resistance. It can also describe someone not showing emotion.
• When 'im-' is added to 'passive', it forms 'impassive'.
• Impassive means not feeling or showing emotion; emotionless.
• In this case, 'im-' acts as a negating prefix, making 'impassive' an antonym of 'passive' (in the sense of showing emotion).

Impertinent: Understanding its Origin

• The word is impertinent.
• The base word is pertinent.
• Pertinent means relevant or applicable to a particular matter; apposite.
• Adding the prefix 'im-' to 'pertinent' creates 'impertinent'.
• Impertinent means not showing proper respect; rude. While its modern meaning focuses on rudeness, historically it derived from 'not pertinent' or 'irrelevant', which can be seen as disrespectful in a social context. Thus, 'impertinent' is an antonym of 'pertinent'.

Imperceptible: Prefix Usage

• The word is imperceptible.
• The base word is perceptible.
• Perceptible means able to be seen or noticed, especially by touch or sight.
• When 'im-' is added to 'perceptible', it forms 'imperceptible'.
• Imperceptible means impossible to perceive or notice.
• Here, 'im-' clearly functions as a negating prefix, making 'imperceptible' the antonym of 'perceptible'.

Impression: Identifying the Outlier

• The word is impression.
• If we try to remove 'im-', we are left with 'pression'. 'Pression' is not a standalone English word from which 'impression' is directly formed as an antonym using 'im-'.
• The word 'impression' comes from Latin 'impressio', meaning "a pressing into," which itself comes from 'imprimere' ("to press into or upon"). In this context, 'im-' is part of the root word and does not act as a negative prefix to form an antonym.
• Impression refers to an idea, feeling, or opinion about something or someone, or an effect produced on the mind or senses. It is a noun that describes an effect or mark, not the opposite of some base word.
• Therefore, 'impression' is the word among the options that is NOT an antonym of another word formed by merely adding the prefix 'im-'.

Conclusion on Prefix Use

Based on the analysis, 'impassive', 'impertinent', and 'imperceptible' are all formed by adding the prefix 'im-' to a base word to create an antonym. However, 'impression' does not follow this pattern; 'im-' is part of its original Latin root and does not function as a negating prefix to create an opposite meaning. Thus, 'impression' is the correct choice as it is NOT an antonym formed by adding the prefix 'im-'.