Boot bottoms (5)
I believe the answer is:
soles
'boot bottoms' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for soles that I've seen before include "Undersides of feet" , "Undersurfaces of feet" , "Shoe bottoms" , "Fish; bottoms of feet" , "They're always under one's feet!" .)