Point to duke heading west
I believe the answer is:
dot
'point' is the definition.
(I know that point can be written as dot)
'to duke heading west' is the wordplay.
'duke' becomes 'd' (abbreviation).
'heading west' shows that the letters should be reversed in order.
'to'+'d'='tod'
'tod' back-to-front is 'DOT'.
(Other definitions for dot that I've seen before include "Full stop, point" , "Spot, speck" , "One signal used in Morse code" , "Little girl" , "Little mark" .)