Here are some other synonyms, depending on the context:
* Hound (used for certain breeds)
* Pup (young dog)
* K9 (military or police term)
* Fido (informal, affectionate)
* Doggy (informal, playful)
Keep in mind that some synonyms have different connotations. For example, "hound" suggests a specific type of dog, while "K9" has a more formal and official tone.