Using the word "deadbeat" as an adjective
BBC quotes President Obama:
America is "not a deadbeat nation", US President Barack Obama has said, as he warned Republicans unconditionally to approve a rise in the US debt ceiling.
It appears to me that deadbeat in this context is an adjective.
The definition of deadbeat lists it solely as a noun. Has President Obama used deadbeat incorrectly?
No, it's fine: any noun can function as an "adjective", for example library in library book.
Technically it's called a noun adjunct or attributive noun and has a Wikipedia entry.