It's about a foot (4)
I believe the answer is:
shoe
'it's about a foot' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for shoe that I've seen before include "Trainer, for instance" , "What one needs for a horse" , "Plate nailed to underside of horse's hoof" , "Case from which playing cards are delt one at a time" , "Oxford, say" .)