Touch a bottom? Almost (4)
I believe the answer is:
abut
'touch' is the definition.
(abutting is a kind of touching)
'a bottom? almost' is the wordplay.
'bottom?' becomes 'butt' ('butt' can be a synonym of 'bottom').
'almost' means to remove the last letter (most of the word but not all of it).
'butt' with its final letter taken away is 'but'.
'a'+'but'='ABUT'
(Other definitions for abut that I've seen before include "Impinge" , "Lie next to" , "Lie adjacent to" , "End or lean against, say a building" , "Lean against the odd tuba" .)