In the following question, out of the four alternatives, choose the one which can be substituted for the given words/sentence. Something that is so deep, intense, or sacred that it cannot be expressed adequately in words.

Introduction / Context:
This question checks your knowledge of precise English vocabulary, especially words that are often used in literature and higher level writing. The phrase given is "that cannot be expressed in words." You are asked to select the single word which captures this idea. Recognizing such words is very useful for reading comprehension and descriptive writing.

Given Data / Assumptions:

• The description is about something that cannot be put into words.
• The focus is on the limitation of language, not on memory, character, or behaviour.
• The options are indelible, ineffable, ingrate, inexorable, and inexpressible.
• We must find the option whose core meaning matches the description most accurately.

Concept / Approach:
The word "ineffable" comes from Latin roots that literally mean "not able to be spoken." In English, ineffable is used for feelings, experiences, or sacred truths that are beyond the power of language to describe. This fits perfectly with the phrase "that cannot be expressed in words." Other options may sound similar but do not carry this specific meaning.

Step-by-Step Solution:
Step 1: Interpret the phrase: it refers to something so profound or intense that language fails to capture it.Step 2: Examine "indelible," which means something that cannot be removed or erased, usually about marks or memories.Step 3: Examine "ineffable," which is defined as too great or extreme to be described in words.Step 4: Examine "ingrate," which refers to an ungrateful person.Step 5: Examine "inexorable," which means impossible to stop or persuade, often applied to fate or a process.Step 6: Match the description to the word; clearly, "ineffable" is the exact fit.

Verification / Alternative check:
Consider a sentence: "The beauty of the sunrise over the mountains was ineffable." Here, ineffable expresses exactly that the beauty could not be fully expressed in words. Substituting "indelible" or "inexorable" would change the meaning completely. Even though "inexpressible" is close in everyday usage, the established one-word substitute in formal vocabulary questions is "ineffable," which is why exam setters prefer it.

Why Other Options Are Wrong:
"Indelible" describes marks or impressions that cannot be erased, not something that cannot be described. "Ingrate" is a noun referring to an ungrateful person and has nothing to do with expression in words. "Inexorable" describes something relentless, such as inexorable progress, but it does not relate to language. "Inexpressible" is a general English word but is not the standard vocabulary term typically tested in this specific one word substitute question, where "ineffable" is the precise choice.

Common Pitfalls:
A common mistake is to choose a word simply because it begins with the prefix "in" and sounds sophisticated. Another pitfall is to confuse "indelible" with "ineffable" because both are used with emotional experiences, such as memories. Carefully linking the root idea "cannot be expressed in words" with "not speakable" helps you remember that "ineffable" is the correct technical term.

Final Answer:
ineffable