I was wondering why the translation for a black cat is 黒猫 and not 黒い猫. It has come to my understanding that 黒い is an adjictive, so that's what should be used when modifying a noun. While 黒 is just a noun.
-
2In the specific case you mentioned, it's because it's a compound word. It's not just a cat that is black (黒い猫 - very much a valid phrase, still), but a black cat. A cat defined by the fact that it's black. – obskyr Jun 27 '17 at 12:47
In short, it's because 黒猫 is an established single word made of two kanji. As you know, a black cat has its own cultural significance in western countries, and this fact is known to Japanese people, too. Someone in the past must have felt it deserved a dedicated single word. It's similar to English words like windmill, airplane, keyboard, etc. 白猫 is also used, but other combinations like 茶猫 or 赤猫 are not common.
黒い猫 means a cat which is black. It's always grammatical to say so, but it may sound a bit clumsy and it may not carry the connotation the word 黒猫 normally has.
