Need a nice authoratative reference for usage of 'Unique'

[stealthsquiggle]

Some silly American is trying to tell me that there can be degrees of uniqueness (I pulled him up on using 'very unique') Does someone have a good online authoritative source I can point him at to shut him up educate him?

Apologies for typo in conversation title

I found this:

u·nique / yoōˈnēk/
? adj. being the only one of its kind; unlike anything else: the situation was unique in modern politics original and unique designs.
∎ particularly remarkable, special, or unusual: a unique opportunity to see the spectacular Bolshoi Ballet. ∎ (unique to) belonging or connected to (one particular person, group, or place): a style of architecture that is unique to Portugal.
? n. archaic a unique person or thing.
DERIVATIVES:
u·nique·ly adv.
u·nique·ness n.

on Encyclopaedia.com, a site which has both UK and US source material.

Thanks - ideally, I want something that explictly says that 'more unique' 'very unique' et al are just plain wrong.

I found this quote - which puts it quite nicely will just have to do until/unless he challenges me on it:

If something is unique, there can be only one. It?s an absolute. It can?t be ?quite unique? or ?very unique?.

Thank you, Minda - exactly what I needed. Unfortunately he has taken the coward's way out and is now ignoring me