Country dispensing with old Conservative PM? (7)

I believe the answer is:

cameron

I'm a little stuck... Click here to teach me more about this clue!

'pm?' is the definition.
(David Cameron, former UK prime minister)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for cameron that I've seen before include "Clan member" , "5,27 [PRIME MINISTER]" , "David --, prime minister" , "Romance (anag) - party leader" , "Conservative leader" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app