>There are about a *dozen* bananas in this basket.
>
>There are about *twelve* bananas in this basket.

I know that there are some adjectives that show quantity. So, *twelve* is an adjective for sure. However, regarding *dozen*, I've some reservations. Oxford dictionary mentions [*dozen* ](http://oald8.oxfordlearnersdictionaries.com/dictionary/dozen)as noun only. 

So I want to know, in the above sentence, is *dozen* a noun or an adjective?