A dog is an animal that many people keep as a pet.
"The dog wagged its tail when I came home."
Related words are connected because they belong to the same idea or topic. They do not have to mean the same thing.
"The puppy loves to play."
"I clipped the leash onto the dog's collar."
"The dog's bark woke me up."
"The dog wagged its tail happily."
"My dog loves to play fetch in the park."
"The dog went into its kennel for a nap."