Knock back some speed, a pill or a tablet (4)
I believe the answer is:
ipad
'a tablet' is the definition.
(tablet made by Apple)
'knock back some speed a pill' is the wordplay.
'knock back' shows that the letters should be reversed in order.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'dapi' is hidden in the letters of 'speed a pill'.
'dapi' back-to-front is 'IPAD'.
'or' acts as a link.
(Other definitions for ipad that I've seen before include "Small personal computer" , "Tablet computer from Apple" .)