Pure Idioms:

These idioms have meanings that cannot be deduced from the meanings of the individual words. They are often metaphorical and their figurative meanings are not immediately apparent from the literal interpretation.

Examples:

• "Kick the bucket": To die. (The words themselves do not provide any clue to the meaning).
• Sentence: "Unfortunately, our old parrot  kicked the bucket last night".
• "Let the cat out of the bag": To reveal a secret accidentally. (The literal words do not explain the figurative meaning).
• Sentence: "She let the cat out of the bag about the surprise party, so now it's no longer a secret".