A young dog, wolf, fox, seal, or shark, or the young of certain other animals.
The dog has had that bed since he was just a pup.
A young, inexperienced person.
The new teacher is a mere pup.
Any cute dog, regardless of age.
My pup likes to run as fast as he can, yet cannot always stop in time!
A short semi-trailer used jointly with a dolly and another semi-trailer to create a twin trailer.