Difference between nouveau and neuf

Question

Why is it “ nouveau copain” and not “copain neuf”? As far as she is concerned he is brand new.

Accepted Answer

Bonjour Alan.
Here are some concrete examples:

Mon nouveau copain = my new friend / boyfriend
Mon nouveau patron = my new boss
Ma nouvelle collègue = my new colleague
Mes nouveaux voisins = my new neighbours
Mon nouvel appartement = my new flat
Ma nouvelle voiture = my new car

In French, you will NEVER use ‘neuf-neuve’ with a living thing, as it sounds like you have just “acquired” him / her recently, like an object ;-) !
Mon copain neuf = my brand new friend
Mon patron neuf = my brand new boss
Attention: ‘neuf – neuve’ = ‘brand new’ (recently build / acquired)

Mon bureau neuf = my brand new desk 
Ma voiture neuve = my brand new car

See link here:new-neuf-versus-nouveau
 
I hope this is helpful.
Bonne journée !

Answer

Don’t think many people would regularly use “brand new” in this context in English either - referring to animate “possessions” as “brand new” sounds odd to me in English or French.

When used in the context of an inanimate possession or abstractions, neuf concisely emphasises the newness or novelty of them, rather than just that they have been newly acquired. Despite that, “tout neuf” is used, just as in English “absolutely brand new” or similar is sometimes used.