Noun

1. A young dog, wolf, fox, seal, shark and some other animals.

   The dog has had that bed since he was just a pup.

2. A young, inexperienced person.

   The new teacher is a mere pup.

3. Any dog that one believes is cute, regardless of age.

   My pup likes to run as fast as he can, yet cannot always stop in time!

4. A short semi-trailer used jointly with a dolly and another semi-trailer to create a twin trailer.