Translation guide
The English word "cold-blooded" has two main meanings: a biological meaning referring to animals that cannot regulate their body temperature, and a figurative meaning describing a person or action that is cruel, unfeeling, or calculated. These meanings are expressed with different Japanese words.
Describing animals like reptiles, fish, and amphibians that rely on external heat sources.
The standard scientific term for an animal whose body temperature changes with the environment. Literally 'variable-temperature animal'. Used in biology and everyday contexts.
Snakes are cold-blooded animals.
Literally 'cold-blooded animal'. This is a direct translation and is understood, but 変温動物 is more common in modern biology. May carry a slightly negative or old-fashioned nuance.
Crocodiles are cold-blooded.
Describing a person, action, or crime that is ruthless, heartless, or done without remorse.
A na-adjective meaning 'cruel', 'cold-hearted', or 'ruthless'. Often used for people or actions that show no mercy.
He is a cold-blooded murderer.
That was a cold-blooded decision.
A na-adjective that directly translates 'cold-blooded'. It is used figuratively but can sound slightly more literal or dramatic than 冷酷な. Often appears in phrases like 冷血漢 (cold-blooded man).
He is a cold-blooded person.
Means 'heartless', 'unfeeling', or 'merciless'. Emphasizes a lack of emotion or compassion. Often used for actions or attitudes.
I received cold-blooded treatment.
Means 'brutal' or 'savage'. Focuses more on the cruelty and violence of an act rather than just coldness. Can overlap with 'cold-blooded' in describing vicious crimes.
It was a cold-blooded crime.
In biology, 変温動物 (poikilotherm) is the preferred term because it accurately describes the variable body temperature. 冷血動物 literally means 'cold-blooded animal' and is less precise, sometimes considered outdated or misleading since these animals' blood isn't actually cold. However, 冷血動物 is still used in everyday language and literature.
While 冷血な can be used figuratively, it is less common than 冷酷な. Using 冷血な might sound like a direct translation from English. For most contexts describing a cruel person or act, 冷酷な is the safer, more natural choice.