Understanding the Phrase

The question asks for a single word that means the same as the phrase "not clear enough to be read". This phrase describes something that is difficult or impossible to read because it's unclear.

Analyzing the Options

Let's look at the meaning of each option provided:

• Corrigible: This word means something or someone is capable of being corrected or reformed. It's often used in contexts like behavior or mistakes. For example, "His bad habits were corrigible." This doesn't fit the meaning of being unreadable.
• Illegible: This word means something is not clear enough to be read. This perfectly matches the meaning of the underlined phrase "not clear enough to be read". For instance, "The old handwriting on the document was illegible."
• Negligible: This word means something is so small or unimportant that it can be ignored. For example, "The risk of failure was negligible." This is unrelated to readability.
• Legible: This word is the opposite of illegible. It means something is clear enough to be read. For example, "Please write in legible print." This is the opposite of what we need.

Identifying the Correct Substitute

Based on the definitions:

• The phrase "not clear enough to be read" describes something that cannot be easily deciphered.
• The word Illegible directly means "not clear enough to be read".
• The other options (Corrigible, Negligible, Legible) have different meanings. Legible is the antonym (opposite).

Therefore, the correct one-word substitute for "not clear enough to be read" is Illegible.