Why "alternate"and not "alternative" CD?

[Colin Law]

On 9 February 2012 23:26, AV3 <arvimide at earthlink.net> wrote:
> On Feb/9/2012 12:1405 PM, Ioannis Vranos wrote:
>>
>> With English not being my native language, I think the proper term for
>> "alternate CD" is "alternative CD". Why "alternate" is used instead?
>>
>>
>
>
> There is little nuance of difference between the two expressions in this
> case. 'Alternative' is an adjective and you understand its meaning
> correctly, Here 'alternate' is a noun;

I did not want to comment on this thread as it is definitely OT and
should be on bikeshed, but I have to say that alternate in this case
is definitely an adjective not a noun.  I don't see how alternate can
ever be a noun, one cannot have "an alternate", only "an alternate
something".

Colin