A different way to join i-adjectives


I originally learned that i-adjectives are joined with くて e.g.

> 長くて、赤い魚が欲しい。

I want a long, red fish.

Recently I've come across a couple of examples where the two adjectives are
joined together with the omission of the い from the first e.g.

> 細長い四角
>
> Thin, long rectangle

Is this something I can do with any pair of i-adjectives or just ones of the
same type (ones that describe size in this case), or are there only specific
pairings that are allowed?




As a general rule, you cannot freely join two arbitrary adjectives like this.
You can't say 長赤い nor 赤長い.

Words like 細長い are sometimes called 複合形容詞 (compound adjective). Here are some
examples:

  * 青白【あおじろ】い (pale), 青【あお】い + 白【しろ】い
  * 赤黒【あかぐろ】い (dark red, bloody), 赤【あか】い + 黒【くろ】い
  * ずる賢【がしこ】い (sly), ずるい + 賢【かしこ】い
  * 暑苦【あつくる】しい (muggy), 暑【あつ】い + 苦【くる】しい
  * 面白【おもしろ】おかしい (funny), 面白【おもしろ】い + おかしい

Basically these words have their own entries in dictionaries.

But once in a while Japanese people coin new words using this rule. For
example young people sometimes say
[キモかわいい](https://www.google.co.jp/search?q=%E3%82%AD%E3%83%A2%E3%81%8B%E3%82%8F%E3%81%84%E3%81%84&source=lnms&tbm=isch)
(gross but cute), which is a fairly new i-adjective made of キモい and かわいい.




As a general rule, you cannot freely join two arbitrary adjectives like this.
You can't say 長赤い nor 赤長い.

Words like 細長い are sometimes called 複合形容詞 (compound adjective). Here are some
examples:

  * 青白【あおじろ】い (pale), 青【あお】い + 白【しろ】い
  * 赤黒【あかぐろ】い (dark red, bloody), 赤【あか】い + 黒【くろ】い
  * ずる賢【がしこ】い (sly), ずるい + 賢【かしこ】い
  * 暑苦【あつくる】しい (muggy), 暑【あつ】い + 苦【くる】しい
  * 面白【おもしろ】おかしい (funny), 面白【おもしろ】い + おかしい

Basically these words have their own entries in dictionaries.

But once in a while Japanese people coin new words using this rule. For
example young people sometimes say
[キモかわいい](https://www.google.co.jp/search?q=%E3%82%AD%E3%83%A2%E3%81%8B%E3%82%8F%E3%81%84%E3%81%84&source=lnms&tbm=isch)
(gross but cute), which is a fairly new i-adjective made of キモい and かわいい.

