Choose the one word that can be substituted for the given phrase: "One who knows everything."

Introduction / Context:
This one word substitution question asks you to find the single word that means "One who knows everything." Such questions often use terms from Latin or Greek roots that commonly appear in advanced English vocabulary. Recognising these roots is a powerful tool in exams and helps you guess meanings accurately even for unfamiliar words.

Given Data / Assumptions:
• Phrase: "One who knows everything." • Options: Omniscient, Conscious, Intellectual, Learned. • The key idea is complete or unlimited knowledge. • The answer will likely contain the element "omni", which often means "all".

Concept / Approach:
"Omniscient" comes from Latin: "omni" meaning all, and "scient" from "scire", meaning to know. So omniscient literally means "all knowing". It is often used as a theological term for a divine being and in literature for a narrator who knows everything about the characters and events. The other options refer to awareness, intelligence, or education but do not convey complete knowledge of everything. Therefore, omniscient is the only word that matches the phrase precisely.

Step-by-Step Solution:
1. Break down the phrase "One who knows everything" into its core idea: complete or unlimited knowledge. 2. Look at the options and recall that "omni" suggests "all". 3. Recognise that "Omniscient" combines "omni" and a root related to knowledge, giving the sense of "all knowing". 4. Examine "Conscious", which simply means aware, usually of one's surroundings or of oneself, not knowing everything. 5. Examine "Intellectual", which describes a person who uses the mind a lot, but not necessarily someone who knows everything. 6. Examine "Learned", which means educated or knowledgeable but again does not imply knowledge of all things.

Verification / Alternative check:
Think of common expressions like "an omniscient narrator" in literature, which describes a narrator who knows everything about the story. Compare this with "a learned person" or "an intellectual", both of which suggest high knowledge but not absolute knowledge. Similarly, "conscious" only relates to awareness, not complete knowledge. This alignment with known usage confirms that omniscient is the best match.

Why Other Options Are Wrong:
Option B, conscious, focuses on awareness and wakefulness, not on knowing all facts or truths. Option C, intellectual, describes a person who engages in serious study or thought but still has limits. Option D, learned, indicates that someone is educated, but there is no suggestion of unlimited or total knowledge. Since the original phrase clearly speaks of someone who knows everything, only omniscient satisfies that condition.

Common Pitfalls:
Some learners may be tempted by "learned" or "intellectual" because they sound impressive and educated. However, these words fall short of meaning "knows everything". Another trap is to misunderstand "omniscient" because it may be less familiar. Learning root words like "omni" (all), "sci" (know), "bene" (good), and "mal" (bad) will help you decode many similar questions rapidly and accurately.

Final Answer:
The correct one word substitute for "One who knows everything" is Omniscient.