Categorial grammar, Is 'leg' an adjective in 'skipping leg days'

I am working on CCG (combinatory categorial grammar), which assigns categories to words.

So I was wondering if 'leg' is adjective, or just another noun in the phrase "skipping leg days". Or is "leg day" a noun phrase by itself? I mean do they combine to become "leg days", or "leg days" is already a form?

CCG would give leg a 'N' tag, and days a 'NP\N'. Meaning, days need a NOUN to its left to combine and become a NOUN PHRASE, that slash in between implies us this. A background info about this combinator is below;

Y : a X\Y : f  ⇒  X : fa         (Backward Application : <)

leg    days
N      NP\N
-----------<
leg days
NP

In leg day, leg is a noun and day is a noun. Leg is an attributive noun (ThoughtCo) or noun adjunct in this noun phrase; it describes the kind of day.

Attributive nouns are commonly used with other nouns to form noun phrases in English. You can even form further noun phrases by using a noun phrase as an attributive noun: Business ethics uses business as an attributive noun; business ethics class uses business ethics as an attributive noun phrase. So you could talk about your leg day schedule, or your leg day routine. It's not hard to generate sentences with multiple noun phrases formed in this way:

After my business ethics class, I took my sports car to the branch office, where I met my Human Resources coworkers for Taco Tuesday margaritas.