Shape or number (6)
I believe the answer is:
figure
I believe this clue is a double definition.
'shape' is the first definition.
(I know that shape can be written as figure)
'number' is the second definition.
(I know that number can be written as figure)
(Other definitions for figure that I've seen before include "form" , "Judge to be probable, estimate" , "The written symbol of a number" , "Reckon" , "movement by skater" .)