Dull pad? (4)

I believe the answer is:

flat

I believe this clue is a double definition.

'dull' is the first definition.
('flat' can be a synonym of 'dull')

'pad?' is the second definition.
(I've seen this before)

(Other definitions for flat that I've seen before include "not deep?" , "One at a meeting" , "without qualification" , "one or more in uniform" , "Pressing implement" .)

I've seen this clue in The Times.

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