Riddle: what word begins and ends with the letter E but usually contains only one letter inside it?

Introduction / Context:
This riddle is built on a play between the idea of letters in words and letters in the postal system. It says that the word begins and ends with E but only has one letter. At first, this seems impossible, because any written word must contain several letters. However, the trick is that one letter refers to a written message that you send by post, not just a single alphabet character. Recognising this double meaning is the key to solving the puzzle.

Given Data / Assumptions:

• The answer is a word that starts with E and ends with E.
• It is associated with containing only one letter, in the postal sense.
• The riddle uses the word letter in its physical mail meaning, not only as a character of the alphabet.
• The object referred to is common in everyday life.
• Among the options, only one word both begins and ends with E and is commonly used to hold letters.

Concept / Approach:
The standard answer is envelope. The word envelope begins with the letter E and ends with the letter E. In everyday life, an envelope is used to hold a letter, meaning a written message on paper. Often, a single letter is placed inside each envelope. So in a punning sense, envelope is a word that begins and ends with E and usually contains one letter inside. Eye and Eve begin and end with E in spelling but they do not literally contain letters, and engine is not associated with mail, so envelope stands out as the correct answer.

Step-by-Step Solution:
List the options and check which ones start and end with the letter E. Envelope starts with E and ends with E. Eye also starts and ends with E, and Eve does as well. Now apply the second clue: the thing has only one letter inside it. Envelope is a container used specifically to hold letters that are sent by mail, often one letter per envelope.

Verification / Alternative check:
Check whether eye or eve contain a letter in the postal sense. Eye is a body part and Eve is a name or word related to the day before an event; neither is used to hold written letters. Engine does not begin and end with E in the same way, and is not linked to letters either. Envelope, however, fits all conditions: correct spelling pattern, and a real life job of storing letters. This dual fit confirms envelope as the riddle's target word and makes it a good example of a simple pun combining spelling and object function.

Why Other Options Are Wrong:
Eye and Eve match the E at the start and end requirement, but they do not function as containers for letters. There is no standard phrase about putting a letter inside an eye or Eve. Engine neither matches the spelling pattern exactly nor the idea of containing a letter. These distractors are there to check whether solvers pay attention to both parts of the clue. Only envelope connects the spelling pattern with the physical job of carrying a single letter in the postal sense.

Common Pitfalls:
A frequent misunderstanding is to interpret only one letter strictly as one alphabet character and then search for a very short word, which is not what the riddle intends. Another issue is to ignore the mail context and stay focused on grammar. To handle riddles like this well, always think about whether key words might have multiple meanings, especially simple words like letter. Once you notice the postal meaning, envelope becomes an obvious and clever answer.

Final Answer:
The word that begins and ends with E and usually contains one letter is envelope.