Spice provided by the eccentric Margaret (6)
I believe the answer is:
nutmeg
'spice' is the definition.
(I know that nutmeg is a spice)
'by the eccentric margaret' is the wordplay.
'by' says to put letters next to each other.
'the eccentric' becomes 'nut' (nut is a kind of eccentric).
'margaret' becomes 'meg' (short for Margaret).
'nut' put next to 'meg' is 'NUTMEG'.
'provided' acts as a link.
(Other definitions for nutmeg that I've seen before include "Spice for grating" , "One grated as spice" , "Spice to grate" , "Aromatic seed - met gnu (anag)" , "put the ball through" .)