Boiling hot, freezing cold, soaking wet and etc are adjective+adjective. So they are compound adjectives. Am I right? Wiktionary says they are idiomatic but I cannot get what is idiomatic? There is also pouring rain that is verb+noun. What is this compound word called too?
Edit: My teacher says boiling in boiling hot act as an adverb. Also he says pouring rain is a set phrase in the following example:
I walked home in the pouring rain and I got soaking wet.