Is there a word for unnecessary adjectives, as in 'a round circle'? My local paper's latest one is 'underwater divers' or am I being pedantic?

It's deja vu all over again!

The word for this is the term:

pleonasm noun. the use of more words than are necessary to convey meaning (e.g., see with one's eyes), either as a fault of style or for emphasis.

Alternatively, you might use a different word, such as, for example,

tautology noun ( pl. -gies) the saying of the same thing twice in different words, generally considered to be a fault of style (e.g., they arrived one after the other in succession).


[url=http://en.wikipedia.org/wiki/Tautology_%28rhetoric%29
]Tautology[/url]

Pleonasm

Note: The unfavourable general consensus about Wikipedia is that it's not very good.

I would say that in the case of "underwater divers", yes, you are being pedantic. You would not include olympic divers or sky divers in the category of underwater divers, or at least I would not. But to answer your question they commented on it in the context of "pilotless drones" (IIRC) over at Language Log some time ago, but I don't have time right now to track it down. You might look around there.

Google is our friend. I googled language-log pilotless-drone and got this page. The term they use for this sort of thing is appositive modification. They have what I believe is a pretty good argument for its not being necessarily an evil, ignorant, stupid practice. The other form of modification is intersective modification.

Welcome aboard Grandad
I don't mind when it is done for emphasis to but it becomes irritating when it is done needlessly for no reason.