I start with 'e' and end with 'e' but contain only one letter. What am I?

This clever word puzzle hinges on a delightful play on the word "letter," which can refer to both a character of the alphabet and a written message. The answer, an envelope, perfectly fits both interpretations. A physical envelope is designed to contain a single piece of correspondence, often called "a letter." Simultaneously, the word "envelope" itself begins with the letter 'e' and concludes with the letter 'e', satisfying all the conditions presented in the riddle.

Envelopes have played a crucial role in human communication for centuries, evolving from simple folded and sealed parchment to the mass-produced paper containers we use today. Their primary purpose is to safeguard the enclosed message and maintain its confidentiality as it travels from sender to recipient. This riddle cleverly exploits the dual meanings inherent in our language, inviting us to consider words from different perspectives and appreciate the nuances that make wordplay so engaging.

Such linguistic brain teasers are more than just fun; they encourage critical thinking and highlight the flexibility and richness of language. They challenge us to look beyond the obvious and explore the various ways words can be interpreted, often leading to a satisfying "aha!" moment when the solution is revealed.