Translation guide
In Japanese, the most common way to say 'pet dog' is 飼い犬 (kainu), which literally means 'a dog one keeps/raises'. The concept of a pet is often expressed through the verb 飼う (kau, 'to keep/raise an animal'), so you can also say ペットの犬 (petto no inu, 'a dog that is a pet') or simply 犬 (inu, 'dog') when context makes it clear. Be careful: the English word 'pet' is sometimes used as a loanword ペット, but it's not always natural to combine it directly with 犬.
The most common, neutral way to refer to a pet dog, without specifying breed or role.
Literally 'a dog one keeps'. This is the standard term for a pet dog, as opposed to a stray or working dog.
うちの飼い犬はとても人懐っこいです。
Our pet dog is very friendly.
飼い犬に手を噛まれる。
To be bitten by one's own pet dog. (proverb: 'to be betrayed by someone you trust')
Uses the loanword ペット (petto) to clarify 'pet'. More explicit but slightly less natural than 飼い犬 in many contexts.
ペットの犬を飼いたいです。
I want to have a pet dog.
Simply 'dog'. Often used when context already implies it's a pet. For example, when talking about your own dog at home.
昨日、犬を散歩に連れて行った。
Yesterday, I took the dog for a walk.
Literally 'beloved dog'. Used to refer to one's own pet dog with affection, often in formal or written contexts, or by dog enthusiasts.
愛犬の健康管理には気をつけています。
I pay attention to my beloved dog's health care.
Emphasizing that the dog lives inside the house as a companion animal, often smaller breeds.
Literally 'indoor dog'. Refers to a dog kept primarily inside the house, often small breeds like Chihuahuas or Toy Poodles.
このアパートでは室内犬を飼えますか？
Can I keep an indoor dog in this apartment?
Literally 'pet dog' in the sense of a companion animal kept for affection. Often used in formal contexts or breed classifications (toy dogs).
Contrasting a pet dog with stray dogs or dogs with specific jobs (police dogs, hunting dogs, etc.).
Again, 飼い犬 is the direct opposite of 野良犬 (stray dog) or 警察犬 (police dog).
この公園は飼い犬のみ入場可です。
Only pet dogs are allowed in this park.
While ペット (petto) is a common loanword, the compound ペット犬 (petto inu) is not standard Japanese. Use 飼い犬 or ペットの犬 instead.
The verb 飼う means 'to keep/raise an animal'. It's the natural way to say you have a pet. For example, 犬を飼っています (inu o katte imasu) means 'I have a dog (as a pet).'
愛玩犬として人気の高いチワワ。
Chihuahuas, which are highly popular as companion dogs.