The common, everyday word for “dog” in Japanese is:

  • 犬（いぬ） → inu = dog

A few other useful related words:

  • 子犬（こいぬ）→ koinu = puppy
  • 飼い犬（かいいぬ）→ kai inu = pet dog
  • 番犬（ばんけん）→ banken = guard dog

In normal conversation, if you just want to say “dog,” 犬（いぬ / inu） is the word you’ll use.