18a) Fatuous importuners driven from site of Macbeth's castle (5)
I - A - E
I'm thinking it must be Inane = Fatuous
Can't quite grasp the importuners from Macbeth's castle bit
Been looking at 'Thanes of Cawdor'
Thinking maybe, In (Th)ane(s) but can't see the connection with the spare (Ths) and importuners.
Any help gratefully welcomed.