Is 'lightning' here a noun or an adjective or even an adverb?

Oxford Dictionaries has this example under ADJECTIVE 'lightning':

(1) Roman is lightning quick and improving every day in practice, and Bean showed playmaking ability in the preseason.

The adjective is categorized in the dictionary as [ATTRIBUTIVE], which the same dictionary defines as:

(Of an adjective or other modifier) preceding the word that it modifies and expressing an attribute, as old in the old dog (but not in the dog is old) and expiry in expiry date. Contrasted with predicative.

At first glance, this lightning in (1) does not seem to be used attributively. For starters, the quick clearly is not a noun modified by the lightning. Then, is it used predicatively somehow not following the dictionary's own categorization as [ATTRIBUTIVE]?

The only possible way to make that happen is as if the lightning were in coordination with the quick. But that's unlikely, because without the quick, it sounds funky:

(1a) Roman is lightning and improving every day in practice, and Bean showed playmaking ability in the preseason. (?)

Merriam-Webster Learner's Dictionary says that lightning in similar cases is an adverb:

— lightning adverb

— used in combination

(2) an athlete with lightning-quick reflexes

(3) making lightning-fast adjustments

This just sounds absurd.

And I'm thinking maybe it's just a noun. But I need some feedback on this. Any thoughts?