Cell with an axon (6)
I believe the answer is:
neuron
'cell with an axon' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for neuron that I've seen before include "Cell that conducts nerve impulses" , "that makes for nervous transmission" , "Conductor" , "Part of one's nervous system" , "Impulsive thing" .)