Fruit tree finally eradicated by 1000 AD (4)

I believe the answer is:

plug

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

'ad' is the definition.
(I know that ad can be written as plug)

I can't explain the rest of the clue.

(Other definitions for plug that I've seen before include "Fitment at the end of a flex" , "Stopper - advert" , "Piece of chewing tobacco" , "Stopper - connector" , "Stopper - advertise" .)

I've seen this clue in The Times and The Sunday Times.

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