Translation guide
A male horse, especially one kept for breeding. In Japanese, the most common word is 種馬, but other terms exist depending on context.
The most common meaning: a male horse used for breeding purposes.
The standard word for a stallion, literally 'seed horse'. Used in both general and technical contexts.
あの牧場には立派な種馬がいる。
That ranch has a fine stallion.
A more technical term used in horse racing and breeding industries. Often seen in formal contexts.
この種牡馬は多くの重賞レースを制した。
This stallion has won many graded stakes races.
Referring to any adult male horse, not necessarily for breeding.
General term for a male horse. Can be used for any adult male horse, but less specific than 種馬.
その雄馬はとても気性が荒い。
That male horse has a very wild temperament.
Another general term for a male horse, often used in written or formal contexts. Can be ambiguous with 種牡馬.
牡馬と牝馬では体格が異なる。
Stallions and mares have different physiques.
Informal, often humorous reference to a sexually potent man.
In slang, 種馬 can refer to a virile man, similar to English 'stallion'. This is informal and may be considered crude.
This usage is very informal and can be offensive. Use only in casual, familiar settings.
彼は自分を種馬だと思っている。
He thinks he's a stallion.
種馬 specifically means a stallion used for breeding. 雄馬 is a general term for any male horse. 牡馬 is also a general term but is more formal/written. In everyday speech, 雄馬 is most common for a male horse, while 種馬 is used when breeding is relevant.
In English, 'stallion' often implies an uncastrated male horse. In Japanese, 雄馬 simply means male horse and does not specify castration status. To be precise about an uncastrated male, you may need to say 去勢していない雄馬 (castrated not male horse).