赤ずきん vs. 赤い頭巾 (grammar)


My understanding is that 赤ずきん refers to the fictional person, "[Little] Red
[Riding] Hood" and 赤い頭巾 refers to the actual object, "red hood". What is the
Japanese grammatical principle in operation here?

Edit: Corrected to '赤い頭巾' from '紅頭巾'




Combining two nouns directly without a particle will introduce a new fixed
concept. That's why 赤ずきん is one fixed idea (it refers to the fictional
character) whereas 赤いずきん refers to a hood that is red. Similar things happen
also in English:

  * blackboard — black board
  * greenhouse — green house
  * smartphone — smart phone

紅頭巾 (wihout い) is not common (why 紅 instead of 赤?), and we need context to
make sense of it. It may be an odd way of writing 赤ずきん, but it may be an
uncommon way of writing 赤いずきん.

See also:

  * [Why isn't 日本料理 written as 日本の料理?](https://japanese.stackexchange.com/q/27485/5010)
  * [-的 adjectives modifying nouns without な](https://japanese.stackexchange.com/q/21150/5010)
  * [the omission of an implied "の" creates the appearance of a 四字熟語{よじじゅくご}?](https://japanese.stackexchange.com/q/19365/5010)




Combining two nouns directly without a particle will introduce a new fixed
concept. That's why 赤ずきん is one fixed idea (it refers to the fictional
character) whereas 赤いずきん refers to a hood that is red. Similar things happen
also in English:

  * blackboard — black board
  * greenhouse — green house
  * smartphone — smart phone

紅頭巾 (wihout い) is not common (why 紅 instead of 赤?), and we need context to
make sense of it. It may be an odd way of writing 赤ずきん, but it may be an
uncommon way of writing 赤いずきん.

See also:

  * [Why isn't 日本料理 written as 日本の料理?](https://japanese.stackexchange.com/q/27485/5010)
  * [-的 adjectives modifying nouns without な](https://japanese.stackexchange.com/q/21150/5010)
  * [the omission of an implied "の" creates the appearance of a 四字熟語{よじじゅくご}?](https://japanese.stackexchange.com/q/19365/5010)

