Automaton dispensing with black base (4)
I believe the answer is:
root
'base' is the definition.
(I know that base can be written as root)
'automaton dispensing with black' is the wordplay.
'automaton' becomes 'robot' (synonyms).
'dispensing with' is a deletion indicator.
'black' becomes 'b' (abbreviation as in pencil classifications).
'robot' with 'b' removed is 'ROOT'.
(Other definitions for root that I've seen before include "Underground part of a plant" , "Underground growth" , "Part of plant drawing nutrients from soil" , "Rummage, origin" , "Origin - stem" .)